Joan of Penthièvre
Joan of Penthièvre (c. 1319–1384), called Joan the Lame, was the only child of Guy of Penthièvre, younger brother of John III of Brittany. In 1337 she married Charles of Blois, and on her uncle's death in 1341 the couple claimed Brittany, fighting the House of Montfort in the Breton War of Succession.
After Charles was killed at Auray in 1364, the Treaty of Guérande in 1365 left her Countess of Penthièvre with a life right to the ducal title.