On 10 Oct 1423 Arthur Montfort III Duke Brittany (age 30) and Margaret Valois (age 29) were married at Dijon. She the daughter of John "Fearless" Valois Duke Burgundy and Margaret Wittelsbach Duchess Burgundy. He the son of John Montfort V Duke Brittany and Joanna of Navarre Queen Consort England (age 53). They were second cousins. He a great x 3 grandson of King Henry III of England. She a great x 4 granddaughter of King Edward "Longshanks" I of England.