Breton Succession, War of the, 1341–65, an important episode of the Hundred Years War. Duke John III of Brittany died in 1341 without heirs. The succession was contested by his half-brother, John de Montfort, who was backed by Edward III of England, and by Charles of Blois, who had married Jeanne de Penthièvre, a niece of the late duke. Charles and Jeanne were supported by Philip VI, John II, and Charles V of France. The resulting war continued through several truces. In the battle of Auray (1364), Charles of Blois was defeated and killed, despite the support of his faithful follower, Bertrand Du Guesclin. The issue was settled by the Treaty of Guérande in 1365, when the Montfort heir was recognized by France as ruler of Brittany. An attempt (1378–79) by Charles V to confiscate Brittany for the French crown met the resistance of the Bretons and of Jeanne de Penthièvre. Du Guesclin, who commanded the royal army, made no serious effort to subdue the Bretons, and the attempt failed.
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