The War of the Breton Succession or Breton Civil War was a conflict between the Counts of Blois and the Montforts of Brittany for control of the Duchy of Brittany. It was fought between 1341 and 12 April 1365. It is also known as the War of the Two Joans due to the involvement of two rival duchesses of that name, Joan of Flanders and Joan of Penthièvre.