John of Montfort

John of Montfort (1294–1345), son of Arthur II of Brittany and Yolande of Dreux, inherited the county of Montfort-l’Amaury from his mother in 1322. When Duke John III died in 1341, he claimed Brittany against his niece Joan of Penthièvre and her husband Charles of Blois, beginning the War of the Breton Succession.

Said to have been urged on by his wife, he rode to Nantes, where the townsmen swore loyalty, and was recognised as duke in May, though the great vassals kept away. Edward III promised military aid.

In September the peers awarded Brittany to Charles, and Philip VI confiscated Montfort-l’Amaury. Nantes fell in November and John was taken to the Louvre. He died in 1345; his wife Joanna of Flanders kept up the fight, and his son John IV later won the duchy.