Duchy of Brittany
The counts of Flanders were also associated with the Duchy of Brittany prior to its union with France. In c 1323, Joan, the daughter of Arthur II, Duke of Brittany, married the second son of Count Robert III. Joanna of Flanders, the granddaughter of Count Robert III and daughter of his son, Count Louis I, married John Montfort. During Montfort's imprisonment, she fought on his behalf, alongside English allies, during the Breton War of Succession for the ducal crown, which was won definitively by her son John V, Duke of Brittany. It was through this alliance that the Duchy of Brittany was eventually joined to the throne of France.