John IV, Duke of Brittany_

John of Montfort, sometimes known as John IV, was Duke of Brittany and Earl of Richmond from 1341 to 1345 in dispute with his niece Joan of Penthièvre and her husband Charles of Blois. He was also Count of Montfort from 1322. He was the son of Arthur II, Duke of Brittany, and his second wife, Yolande of Dreux. His contesting of the inheritance of the Duchy of Brittany with his niece Joan led to the War of the Breton Succession, which in turn evolved into being part of the Hundred Years' War between England and France. John's patron in his quest was King Edward III of England. He died in 1345, 19 years before the end of the war, and the victory of his son John IV, Duke of Brittany, over Joan of Penthièvre and Charles of Blois.