England dominated the English Channel for the rest of the war, preventing French invasions. At this point, Edward's funds ran out and the war probably would have ended were it not for the death of the Duke of Brittany in 1341 precipitating a succession dispute between the duke's half-brother John of Montfort and Charles of Blois, nephew of Philip VI.

In 1341, conflict over the succession to the Duchy of Brittany began the War of the Breton Succession, in which Edward backed John of Montfort (male heir) and Philip backed Charles of Blois (female heir) . Action for the next few years focused around a back-and-forth struggle in Brittany. The city of Vannes in Brittany changed hands several times, while further campaigns in Gascony met with mixed success for both sides. The English-backed Montfort finally succeeded in taking the duchy but not until 1364. The war formed an integral part of the early Hundred Years' War due to the proxy involvement of the French and English governments in the conflict.