Before 14 Jul 1310 [her father] Henry Beaumont Earl Buchan (age 31) and [her mother] Alice Comyn Baroness Beaumont were married. She by marriage Baroness Beaumont. He by marriage Earl Buchan. He a great x 3 grandson of King Henry I "Beauclerc" England.

Around 1320 Isabel Beaumont Duchess Lancaster was born to Henry Beaumont Earl Buchan (age 41) and Alice Comyn Baroness Beaumont.

Around 1328 Henry of Grosmont 1st Duke Lancaster (age 18) and Isabel Beaumont Duchess Lancaster (age 8) were married. She the daughter of Henry Beaumont Earl Buchan (age 49) and Alice Comyn Baroness Beaumont. He the son of Henry Plantagenet 3rd Earl of Leicester 3rd Earl Lancaster (age 47) and Maud Chaworth. They were fourth cousins. He a great grandson of King Henry III of England. She a great x 4 granddaughter of King Henry I "Beauclerc" England.

On 06 Nov 1330 [her brother] John Beaumont 2nd Baron Beaumont (age 12) and [her sister-in-law] Eleanor Plantagenet Countess Arundel and Surrey (age 12) were married. She the daughter of [her father-in-law] Henry Plantagenet 3rd Earl of Leicester 3rd Earl Lancaster (age 49) and Maud Chaworth. He the son of [her father] Henry Beaumont Earl Buchan (age 51) and [her mother] Alice Comyn Baroness Beaumont. They were fourth cousins. He a great x 4 grandson of King Henry I "Beauclerc" England. She a great granddaughter of King Henry III of England.

In 1337 [her husband] Henry of Grosmont 1st Duke Lancaster (age 27) was created 1st Earl Lincoln. Isabel Beaumont Duchess Lancaster (age 17) by marriage Countess Lincoln.

On 10 Mar 1340 [her father] Henry Beaumont Earl Buchan (age 61) died at Buchan. His son [her brother] John Beaumont 2nd Baron Beaumont (age 22) succeeded 2nd Baron Beaumont. [her sister-in-law] Eleanor Plantagenet Countess Arundel and Surrey (age 21) by marriage Baroness Beaumont.

On or before 04 Apr 1340 [her daughter] Maud Plantagenet Duchess Lower Bavaria was born to [her husband] Henry of Grosmont 1st Duke Lancaster (age 30) and Isabel Beaumont Duchess Lancaster (age 20) at Bolingbroke Castle, Lincolnshire [Map]. The exact date of her birth uncertain. The Inquisition of her father in May 1361 refers to Blanche being "Maud lady of Henaud [Hainault], aged 21 years on the feast of St. Ambrose last". The Feast of the Ambrose being the 4th of April so Maud was born on or before the 4th of April 1340. She a great x 2 granddaughter of King Henry III of England.

On or before 25 Mar 1342 [her daughter] Blanche Duchess of Lancaster was born to [her husband] Henry of Grosmont 1st Duke Lancaster (age 32) and Isabel Beaumont Duchess Lancaster (age 22) at Bolingbroke Castle, Lincolnshire [Map]. The exact date of her birth uncertain. The Inquisition of her father in May 1361 refers to Blanche being "aged 19 years at the feast of the Annunciation last". The Feast of the Annunciation being the 25th of March so Blanche was born on or before the 25th of March 1342. She a great x 2 granddaughter of King Henry III of England.

In 1344 [her son-in-law] Ralph Stafford and [her daughter] Maud Plantagenet Duchess Lower Bavaria (age 3) were married. She the daughter of [her husband] Henry of Grosmont 1st Duke Lancaster (age 34) and Isabel Beaumont Duchess Lancaster (age 24). He the son of Ralph Stafford 1st Earl Stafford (age 42) and Margaret Audley Countess Stafford (age 26). They were third cousin once removed. He a great x 2 grandson of King Edward I of England. She a great x 2 granddaughter of King Henry III of England.

14 Dec 1344 Richard Fitzalan 10th Earl of Arundel 8th Earl of Surrey (age 38) and Isabel Despencer Countess Arundel (age 32) marriage annulled by Pope Clement VI on the grounds that he had never freely consented to marry Isabel. He, at this time, is believed to be having an affair with her first cousin [her sister-in-law] Eleanor (age 26) who he married four months later.

In or before 1345 Ralph Ufford (age 42) and [her sister-in-law] Maud Plantagenet Countess Ulster (age 34) were married. She the daughter of [her father-in-law] Henry Plantagenet 3rd Earl of Leicester 3rd Earl Lancaster (age 63) and Maud Chaworth. She a great granddaughter of King Henry III of England.

On 05 Apr 1345 Richard Fitzalan 10th Earl of Arundel 8th Earl of Surrey (age 39) and [her sister-in-law] Eleanor Plantagenet Countess Arundel and Surrey (age 26) were married at Ditton Church, Stoke Poges. She by marriage Countess Arundel Sussex. She the daughter of [her father-in-law] Henry Plantagenet 3rd Earl of Leicester 3rd Earl Lancaster (age 64) and Maud Chaworth. He the son of Edmund Fitzalan 9th Earl of Arundel and Alice Warenne Countess Arundel. They were half third cousins. He a great x 5 grandson of King John of England. She a great granddaughter of King Henry III of England.

In Jun 1347 John Warenne 7th Earl of Surrey (age 60) died. His nephew Richard Fitzalan 10th Earl of Arundel 8th Earl of Surrey (age 41) succeeded 8th Earl Surrey. [her sister-in-law] Eleanor Plantagenet Countess Arundel and Surrey (age 28) by marriage Countess Surrey. Conisbrough Castle [Map] reverted to the Crown.

In 1349 [her husband] Henry of Grosmont 1st Duke Lancaster (age 39) was created 1st Earl Derby. Isabel Beaumont Duchess Lancaster (age 29) by marriage Countess Derby.

In 1351 [her husband] Henry of Grosmont 1st Duke Lancaster (age 41) was created 1st Duke Lancaster by King Edward III of England (age 38). Isabel Beaumont Duchess Lancaster (age 31) by marriage Duchess Lancaster.

In 1352 [her son-in-law] William Wittelsbach I Duke Lower Bavaria (age 21) and [her daughter] Maud Plantagenet Duchess Lower Bavaria (age 11) were married in London. She by marriage Duchess Lower Bavaria. He by marriage Earl of Leicester. She the daughter of [her husband] Henry of Grosmont 1st Duke Lancaster (age 42) and Isabel Beaumont Duchess Lancaster (age 32). He the son of Louis Wittelsbach IV Holy Roman Emperor and Margaret Hainault Holy Roman Empress (age 40). He a great x 4 grandson of King Henry "Curtmantle" II of England. She a great x 2 granddaughter of King Henry III of England.

In 1361 Isabel Beaumont Duchess Lancaster (age 41) died.