Jean IV de Montfort, duc de Bretagne

http://genealogics.org/getperson.php?personID=I00004907&tree=LEO

https://fr.wikipedia.org/wiki/Jean_IV_de_Bretagne

John IV of Montfort (in Breton Yann Moñforzh, in French Jean de Montfort) (1295 – 16 September 1345 Château d'Hennebon), was duke of Brittany, from 1341 to his death. He was son of Duke Arthur II and Yolande de Dreux, countess of Montfort, his second wife.

Marriage and issue

In 1322 he succeeded his mother as count of Montfort, and in 1329, he married Joanna of Flanders at Chartres. They had two children:

John V, Duke of Brittany (1339–1399)

Joan of Brittany, Baroness of Drayton (1341 – aft. 20 October 1399), married before 21 October 1385 Ralph Basset, 4th Baron Basset de Drayton
Breton War of Succession

When his half-brother, duke John III, died with no male heirs in 1341, John IV decided to contest the rights of his niece, Joanna of Penthièvre, and her husband, Charles of Blois, to the duchy of Brittany. This led to the Breton War of Succession part of the Hundred Years' War. His patron in this quest was king Edward III of England.

Ancestry

http://en.wikipedia.org/wiki/John_IV,_Duke_of_Brittany#Ancestry