Mistress
Mistress is in General Things.
1520 Marriage of William Carey and Mary Boleyn
1600 Wedding of Henry Somerset and Anne Russell
In 1177 Cardinal Peter of Saint Chrysogonus, on behalf of the Pope, threatened to place England's continental possessions under an interdict if Henry did not proceed with the marriage. King Richard "Lionheart" I of England (age 19) was somewhat reluctant given the rumours that Alys Capet Countess Ponthieu (age 16) had become the mistress of his father King Henry "Curtmantle" II of England (age 43) and, possibly, had a child by him.
In 1336 King Robert II of Scotland (age 19) and Elizabeth Mure Queen Consort Scotland were married. She by marriage Queen Consort Scotland. She had been his mistress for a number of years. He a great x 3 grandson of King John "Lackland" of England. 
On 18 Aug 1471 George Gordon 2nd Earl Huntley (age 16) and Elizabeth Hay Countess Huntley (age 21) were married; she having been his mistress. She by marriage Countess Huntley. She the daughter of William Hay 1st Earl Erroll and Beatrice Douglas Countess Erroll. He the son of Alexander Gordon 1st Earl Huntley and Elizabeth Crichton Countess Huntley (age 61).
Around 1495 Margaret Drummond (age 20) became a mistress to King James IV of Scotland (age 21).
Around 1509 Joan Larke (age 19) became the mistress of Cardinal Thomas Wolsey (age 35).
Around 1515 Elizabeth "Bessie" Blount Baroness Clinton and Tailboys (age 17) became the mistress of King Henry VIII of England and Ireland (age 23). Their relationship continued until around 1520, possibly longer, when she was replaced by Mary Boleyn (age 16).
Around 1520 Marion Ogilvy (age 25) became the mistress of Cardinal David Beaton (age 26).
On 04 Feb 1520 William Carey (age 20) and Mary Boleyn (age 21) were married. Around the time, possibly shortly after, Mary Boleyn (age 21) became mistress to King Henry VIII of England and Ireland (age 28) leading to speculation one or both of her children were fathered by Henry (age 28). She the daughter of Thomas Boleyn 1st Earl Wiltshire and Ormonde (age 43) and Elizabeth Howard Countess of Wiltshire and Ormonde (age 40). He a great x 4 grandson of King Edward III of England. 
The evidence for Mary being Henry's mistress:
Letters and Papers Foreign and Domestic. 20 Oct 1537. George Throckmorton letter relating to events around 1531 where Henry responds to an accusation that he had relationships with both Anne Boleyn's mother and sister "Never with the mother". Cromwell goes on the say never with the sister either.
Defense of the Unity of the Church Book III, 1536, letter from Cardinal Reginald Pole to King Henry VIII accusing him of double standards by attempting to annul his marriage with Queen Katherine on the basis of her having previously been married, albeit unconsummated, to Henry's brother Arthur, as a means to allow Henry to marry Anne Boleyn, with who sister Henry had had a carnal relationship.
1536 Letter from Ambassador Chapuys to the Emperor in which Chapuys writes "Others tell me that the said Archbishop had pronounced the marriage of the King and Concubine [Anne] invalid on account of the King having had connection with her sister [Mary].
On 18 Jun 1522 Gilbert Tailboys 1st Baron Tailboys (age 24) and Elizabeth "Bessie" Blount Baroness Clinton and Tailboys (age 24) were married. She the former mistress of King Henry VIII of England and Ireland (age 27) had given given birth to Henry's illegitimate son Henry Fitzroy 1st Duke Richmond and Somerset in Jun 1519. He a great x 5 grandson of King Edward III of England. 
Around 1534 Diane de Poitiers (age 33) became the mistress of King Henry II of France (age 14).
From Feb 1535 Margaret "Madge" Shelton was believed to have been a mistress of King Henry VIII of England and Ireland (age 43). Eustace Chapuys (age 45) refers to "Mistress Shelton". Others have suggested "Mistress Shelton" could be Madge's sister Mary Shelton (age 25).
On 28 Apr 1573 Charles Valois Duke Angoulême was born illegitimately to Charles IX King France (age 22) and Marie Touchet (age 24). The only child of Charles IX King France (age 22). She, Marie Touchet (age 24), would subsequently marry and have issue two daughters, Catherine Henriette de Balzac d'Entragues and Marie Charlotte de Balzac d'Entragues who were both mistresses to Henry IV King France (age 19).
Around 1580 Anne Vavasour (age 20) became the mistress of Edward de Vere 17th Earl of Oxford (age 29). The affair led to open skirmishes and duels in the streets of London, between Oxford and Anne's uncle, Thomas Knyvet 1st Baron Knyvet (age 35), and his men, which on one occasion led to the wounding of both men, and the death of one of Oxford's men.
Before 1581 James Gray and Elizabeth Bethune were married. They were divorced in 1581 since she had become mistress to King James V of Scotland.
Before 1590 Anne Vavasour (age 30) became the mistress of Henry Lee of Ditchley (age 56).
On 16 Jun 1600 Henry Somerset 1st Marquess Worcester (age 23) and Anne Russell 2nd Marchioness Worcester (age 22) were married. He the son of Edward Somerset 4th Earl of Worcester (age 50) and Elizabeth Hastings Countess of Worcester (age 54).
Mary Fitton (age 21) led a Masque in celebration at the Blackfriars residence of Henry Brooke 11th Baron Cobham (age 35) with Queen Elizabeth I of England and Ireland (age 66) and William Herbert 3rd Earl Pembroke (age 20) attending. She, Mary soon afterwards became the mistress of William Herbert 3rd Earl Pembroke (age 20) and soon became pregnant.
From 1605 to 1609 Marie Charlotte de Balzac d'Entragues (age 21) was mistress to Henry IV King France (age 51).
In 1609 Henry Bourbon Condé II Prince Condé (age 20) and Charlotte Marguerite Montmorency Princess Condé (age 14) were married. She by marriage Princess Condé. A marriage arranged by Henry IV King France (age 55) who wanted her for a mistress; the couple travelled to Brussels to avoid his attention. He the son of Henri Bourbon Condé Prince Condé and Charlotte Catherine Tremoille Princess Condé.
On 06 Jan 1658 Charles Louis Palatinate Simmern (age 40) and Maria Susanne Luise von Degenfeld (age 23) were married morganatically. She had previously been his mistress. As a result of the marriage being morganatic their children were excluded from the succession. He the son of Frederick Palatinate Simmern V Elector Palatine Rhine and Princess Elizabeth Stewart Queen Bohemia (age 61). He a grandson of King James I of England and Ireland and VI of Scotland. 
On 11 Dec 1661 Roger Palmer 1st Earl Castlemaine (age 27) was created 1st Earl Castlemaine, 1st Baron Limerick by King Charles II of England Scotland and Ireland (age 31) in gratitude for allowing his wife Barbara Villiers 1st Duchess of Cleveland (age 21) to become the King's mistress. Barbara Villiers 1st Duchess of Cleveland (age 21) by marriage Countess Castlemaine.
Around 1662 Winifred Wells Maid of Honour (age 20) became a mistress of King Charles II of England Scotland and Ireland (age 31).
Around 1665 Arabella Churchill (age 15) became the mistress of King James II of England Scotland and Ireland (age 31).
In 1665 John Denham (age 50) and Margaret Brooke Lady Denham (age 25) were married. She, thereafter, conducted a very public affair with the future King James II (age 31). To her husband's mortification, she insisted on being acknowledged publicly as a Royal mistress, saying that she would not, unlike her predecessor Goditha Price "go up and down the back stairs". The difference in their ages was 25 years.
Around 1667 Diana Kirke Countess of Oxford became the mistress of Aubrey de Vere 20th Earl of Oxford (age 39).
Around 1667 Mary "Moll" Davis (age 19) became a mistress of King Charles II of England Scotland and Ireland (age 36).
Before 1672 Louise Kéroualle 1st Duchess Portsmouth (age 22) became a mistress of King Charles II of England Scotland and Ireland (age 41).
In 1673 Margaret "Peg" Hughes (age 43) became the mistress of Prince Rupert Palatinate Simmern 1st Duke Cumberland (age 53).
On 19 Aug 1673 Louise Kéroualle 1st Duchess Portsmouth (age 23) was created 1st Duke Portsmouth, 1st Earl Fareham, 1st Baron Petersfield by King Charles II of England Scotland and Ireland (age 43) for life for being his mistress and for having given birth to his son Charles Lennox 1st Duke Richmond (age 1).
Around 1674 Henri Gascar (age 39) came to England, probably at the request of Louise Kéroualle 1st Duchess Portsmouth (age 24), mistress of Charles II King Scotland.
Around 1675 Mary Beale aka Cradock (age 41). Portrait of Lady Norwich. Probably Jane Bickerton Duchess Norfolk (age 32) who married the Duke around 1675 being his mistress prior to their marriage.
Before 1676 Catherine Sedley Countess Dorchester and Portmore (age 18) became the mistress of King James II of England Scotland and Ireland (age 42).
Around Jun 1676 Hortense Mancini Duchess of Mazarin (age 29) had become the mistress of King Charles II of England Scotland and Ireland (age 46) for whom he had provided a pension of £4000 each year.
In 1686 Catherine Sedley Countess Dorchester and Portmore (age 28) was created 1st Earl Dorchester for life by King James II of England Scotland and Ireland (age 52) for services as his mistress. Her father Charles Sedley 5th Baronet (age 46) quipped "As the king (age 52) has made my daughter a countess, the least I can do, in common gratitude, is to assist in making his Majesty's daughter (age 23) a queen".
In 1691 Edward Villiers 1st Earl Jersey (age 35) was created 1st Viscount Villiers, 1st Baron Villiers probably as a consequence of his sister Barbara Villiers Viscountess Fitzhardinge (age 37) being a mistress of King William III of England, Scotland and Ireland (age 40). Barbara Chiffinch Countess Jersey (age 28) by marriage Viscountess Villiers.
In 1697 Edward Villiers 1st Earl Jersey (age 41) was created 1st Earl Jersey probably as a consequence of his sister Barbara Villiers Viscountess Fitzhardinge (age 43) being a mistress of King William III of England, Scotland and Ireland (age 46). Barbara Chiffinch Countess Jersey (age 34) by marriage Countess Jersey.
In 1698 David Colyear was born to David Colyear 1st Earl Portmore (age 42) and Catherine Sedley Countess Dorchester and Portmore (age 40). Given his mother was a recent mistress of King James II of England Scotland and Ireland (age 64) it is possible the father was King James II of England Scotland and Ireland (age 64).
On 27 Aug 1700 Charles Colyear 2nd Earl Portmore was born to David Colyear 1st Earl Portmore (age 44) and Catherine Sedley Countess Dorchester and Portmore (age 42). Given his mother was a recent mistress of King James II of England Scotland and Ireland (age 66) it is possible the father was King James II of England Scotland and Ireland (age 66).
On 13 Apr 1703 David Colyear 1st Earl Portmore (age 47) was created 1st Earl Portmore. Possibly for having married the King's former mistress Catherine Sedley Countess Dorchester and Portmore (age 45). Catherine Sedley Countess Dorchester and Portmore (age 45) by marriage Countess Portmore.
Around 1706 Frances Stewart became the mistress of John Sheffield 1st Duke of Buckingham and Normanby (age 57).
In 1714 Henrietta Hobart Countess Suffolk (age 25) became the mistress of King George II of Great Britain and Ireland (age 30).
Before 1732 Anne Vane became the a mistress of Frederick Louis Hanover Prince of Wales (age 24).
On 25 Dec 1744 Henry Brydges 2nd Duke Chandos (age 36) and Anne Wells Duchess Chandos were married at Keith's Chapel, Mayfair. She by marriage Duchess Chandos. Two versions of their meeting are related... He the son of James Brydges 1st Duke Chandos and Mary Lake.
Notes & Queries 1870 4th Series, Vol. 6, p.179: Lord Omery remarked, on 15th January 1745, "Of her person & character people speak variously, but all agree that both are very bad. " He was speaking of Anne, Duchess of Chandos. She was the daughter of one John Wells of Newbury (& St. Marylebone) whose arms appear as azure, three fountains proper, on her hatchment at Keynsham Church. She was chambermaid at the Pelican Inn Newbury, and married to Jeffries the Ostler there. There is a story about the Duchess told by an old lady of Newbury, who was ten years old at the time. Henry Bridges, 2nd Duke of Chandos (age 36), while on his way to London, dined at the Pelican Inn in Newbury, with a companion (it has been claimed that the Inn was the Marlborough Castle, but this is incorrect). After dinner there was a stir and a bustle in the Inn Yard. The explanation came that "A man is going to sell his wife and they are leading her up the yard with a halter round her neck". "We will go and see the sale, " said the Duke. On entering the yard, however, he was so smitten with the woman's beauty and the patient way she waited to be set free from her ill‑conditioned husband, the Inn's ostler, that he bought her himself. She was his mistress for some years. In August 1738 his wife died, and by 1744 the ostler was dead also, and the two were finally married at Mr. Keith's Chapel, Mayfair on 25th December 1744.
The Gentleman's Magazine 1832. The Duke of Chandos (age 36), while staying at a small country inn, saw the ostler beating his wife in a most cruel manner; he interfered and literally bought her for half a crown. She was a young and pretty woman; the Duke had her educated; and on the husband's death he married her. On her death-bed, she had her whole household assembled, told them her history, and drew from it a touching moral of reliance on Providence; as from the most wretched situation, she had been suddenly raised to one of the greatest prosperity; she entreated their forgiveness if at any time she had given needless offence, and then dismissed them with gifts; dying almost in the very act.
Before 1748 Robiana Brown became the mistress of Charles Mordaunt 4th Earl Peterborough 2nd Earl Monmouth (age 39).
On 23 Mar 1769 Augustus Henry Fitzroy 3rd Duke Grafton (age 33) and Anne Liddell Duchess Grafton (age 32) were divorced when he discovered she was pregnant by her lover John Fitzpatrick 2nd Earl Upper Ossory (age 23) whom she subsequently married. Plans to marry his mistress Anne aka Nancy Parsons Viscountess Maynard (age 34), if they existed, were undermined by the the discovery he discovered she was having an affair with John Frederick Sackville 3rd Duke Dorset (age 23).
In or before 1783 Banastre Tarleton 1st Baronet (age 28) and Mary "Perdita" Darby aka Robinson (age 25) had a relationship. She the former mistress of King George IV of Great Britain and Ireland (age 20).
In 1785 Elizabeth Ilive Countess Egremont (age 16) became the mistress of George O'Brien Wyndham 3rd Earl Egremont (age 33).
In 1788 William Elector of Hesse (age 44) abducted Caroline Countess of Schlotheim (age 22) and made her his mistress.
In 1792 Henry Crewe 7th Baronet (age 29) and Ann or Nanny Hawkins were married. She having been his mistress.
In 1807 Francis Ingram Seymour-Conway 2nd Marquess Hertford (age 63) took his wife Isabella Anne Ingram Marchioness Hertford (age 47) to Ireland in an attempt to prevent King George IV of Great Britain and Ireland (age 44) taking her as a mistress. By the summer King George IV of Great Britain and Ireland (age 44) was a regular visitor at Ragley Hall Alcester and Hertford aka Manchester House Manchester Square Marylebone.
Around 1819 Elizabeth Denison Marchioness Conyngham (age 49) replaced Isabella Anne Ingram Marchioness Hertford (age 59) as the mistress of King George IV of Great Britain and Ireland (age 56).
1853. William Holman Hunt (age 25). "Awakening Conscience". A mistress realises the undesirability of her actions. Note the absence of a wedding ring on her finger. Hunt hired a room at 7 Alpha Place, a "maison de convenance" to complete the painting. The painting has many symbols: the cat toying with the broken-winged bird under the table symbolises the woman's plight, a man's discarded glove warns that the likely fate of a cast-off mistress was prostitution, a tangled skein of yarn on the floor symbolises the web in which the girl is entrapped. The frame, designed by Hunt, also contains various symbolic emblems; the bells and marigolds stand for warning and sorrow, the star is a sign of spiritual revelation. [Source. Tate]. The model is Annie Miller (age 18).
1858. Frederick Sandys (age 28). "Queen Eleanor". Note the cup of poison in her right hand and the dagger in her left hand with which she would offer Rosamund, mistress of her husband Henry II, a choice as to how to die.
On 20 Sep 1858 James Brudenell 7th Earl Cardigan (age 60) and Adeline Horsey Countess Cardigan (age 33) were married after having been his mistress. She by marriage Countess Cardigan. The marriages something of a scandal since James Brudenell 7th Earl Cardigan (age 60) had left his first wife; Queen Victoria of the United Kingdom (age 39) refused to have her at court. The difference in their ages was 27 years. He the son of Robert Brudenell 6th Earl Cardigan and Penelope Cooke Countess Cardigan.
After 11 Jun 1864 Susan Charlotte Catherine Pelham-Clinton (age 25) became the mistress of King Edward VII of the United Kingdom (age 22). She is believed by some to have had a child with the Prince although evidence is scant.
Around 1872 Olivia Taylour unsuccessfully attempted, allegedly, to become the mistress of Prince Albert Saxe Coburg Gotha. Around the same time her daughter Mary "Patsy" Fitzpatrick (age 16), aged sixteen, became the mistress of his son King Edward VII of the United Kingdom (age 30). She, Patsy, was married off to William Cornwallis-West (age 36).
On 30 Apr 1884 father and daughter, Prince Louis Hesse Darmstadt IV Grand Duke (age 46) and Victoria Hesse Darmstadt Marchioness Milford Haven (age 21), were both married on the same, of near, days, he taking advantage pf his relatives being in Darmstadt for his daughter's wedding. He, apparently, didn't approve of his daughter's choice of his first cousin Prince Louis of Battenburg 1st Marquess Milford Haven (age 29) since they, Prince Louis of Battenburg 1st Marquess Milford Haven (age 29) and Victoria Hesse Darmstadt Marchioness Milford Haven (age 21) would live in Britain.
Prince Louis of Battenburg 1st Marquess Milford Haven (age 29) and Victoria Hesse Darmstadt Marchioness Milford Haven (age 21) were married. She the daughter of Prince Louis Hesse Darmstadt IV Grand Duke (age 46) and Princess Alice Saxe Coburg Gotha. They were first cousin once removed. She a granddaughter of Queen Victoria of the United Kingdom.
In the evening Prince Louis Hesse Darmstadt IV Grand Duke (age 46) and Alexandrina Hutten Czapska (age 29) were married. She being his former mistress. Apparently, they separated within a week and the marriage was annulled within three months.
Around 1898 Alice Frederica Edmonstone aka Keppel (age 29) became the mistress of King Edward VII (age 56). She remained his mistress for the remainder of his life.
On 24 May 1900 Sonia Rosemary Keppel was born to George Keppel (age 34) and Alice Frederica Edmonstone aka Keppel (age 32). Given that she was at the time the mistress of King Edward VII (age 58) there is some uncertainty as to whether George Keppel (age 34) was her father.
On 30 Dec 1915 the SS Persia was torpedoed near Crete without warning by the German U-boat U-38, commanded by Max Valentiner. It sank in five to ten minutes, killing 343 of the 519 aboard.
John Douglas-Scott-Montagu 2nd Baron Montagu of Beaulieu (age 49) survived. His mistress Eleanor Thornton (age 35) drowned.
