War of the Breton Succession
Blois was associated with Champagne Province, the House of Châtillon (who tended to reside in Blois), the Dukes of Brittany and, later, with the French royal family. Theobald I, Count of Blois served as Regent to Drogo, Duke of Brittany. Bertha of Blois, the daughter of Odo II of Blois, became Duchess Consort of Brittany through her marriage to Alan II, Duke of Brittany. Stephen Henry's son Stephen of Blois became King of England. Charles de Blois, son of Guy I, Count of Blois, married Joan of Penthievre, the heiress of John III, Duke of Brittany; together, they became principal protagonists in the War of the Breton Succession. Upon the death of his only son, Guy II, Count of Blois sold the county to Louis I, Duke of Orléans and the county passed to the French royal family.