On 22 Jan 1260 [his father] John Capet II Duke Brittany (age 21) and [his mother] Beatrice Plantagenet (age 17) were married. She the daughter of King Henry III of England (age 52) and Eleanor of Provence Queen Consort England (age 37). He the son of John "The Red" Capet I Duke Brittany (age 42) and Blanche "Navarre" Blois Duchess Brittany (age 34). They were half second cousin twice removed. He a great x 5 grandson of King William "Conqueror" I of England.

In 1275 Arthur Capet Duke Brittany (age 13) and Marie Limoges Duchess Brittany were married. She by marriage Duchess Brittany 1221 Dreux. He the son of John Capet II Duke Brittany (age 36) and Beatrice Plantagenet (age 32). They were third cousins. He a grandson of King Henry III of England.

On 15 Oct 1285 Alexander III King Scotland (age 44) and [his future wife] Yolande Capet Duchess Brittany (age 24) were married. She the daughter of Robert Capet IV Count Dreux and Beatrice Montfort Countess Dreux (age 36). He the son of Alexander II King Scotland and Marie Coucy. They were half second cousin twice removed. He a great x 3 grandson of King Henry I "Beauclerc" England. She a great x 5 granddaughter of King Henry I "Beauclerc" England.

In or before 1295 Arthur Capet Duke Brittany (age 33) and Yolande Capet Duchess Brittany (age 33) were married. She by marriage Duchess Brittany 1221 Dreux. She the daughter of Robert Capet IV Count Dreux and Beatrice Montfort Countess Dreux (age 46). He the son of John Capet II Duke Brittany (age 55) and Beatrice Plantagenet. They were third cousins. He a grandson of King Henry III of England. She a great x 5 granddaughter of King Henry I "Beauclerc" England.

In 1297 [his son] John Capet III Duke Brittany (age 10) and [his daughter-in-law] Isabelle Valois Duchess Brittany (age 5) were married. She by marriage Duchess Brittany 1221 Dreux. She the daughter of Charles Valois I Count Valois (age 26) and Margaret Capet Countess Valois (age 24). They were third cousins. He a great grandson of King Henry III of England. She a great x 4 granddaughter of King Henry "Curtmantle" II of England.

In 1310 [his son] John Capet III Duke Brittany (age 23) and [his daughter-in-law] Isabella Ivrea Queen Consort Aragon (age 27) were married. She by marriage Duchess Brittany 1221 Dreux. She the daughter of Sancho IV King Castile IV King Leon and Maria Molina Queen Consort Castile Queen Consort Leon. He a great grandson of King Henry III of England. She a great x 4 granddaughter of King Henry "Curtmantle" II of England.

John "Good" Capet and Perrenelle Sully were married. He the son of Robert Capet IV Count Dreux and Beatrice Montfort Countess Dreux. He a great x 5 grandson of King Henry I "Beauclerc" England.

Robert Dampierre Count Marle and [his daughter] Joan Montfort were married. He the son of Robert Dampierre III Count Flanders and Yolande Burgundy II Countess Nevers and Flanders. They were third cousins. She a great granddaughter of King Henry III of England.

John "Good" Capet and Jeanne Montpensier were married. He the son of Robert Capet IV Count Dreux and Beatrice Montfort Countess Dreux. He a great x 5 grandson of King Henry I "Beauclerc" England.

Guy 10th de Laval Baron and [his daughter] Beatrice Montfort were married. She a great granddaughter of King Henry III of England.