House of Blois chose a wife from the House of Champagne (Adela of Champagne) as a counterpoise to Angevin power. The senior line of the House of Blois became extinct with the death of Joan I of Navarre, wife of Philip IV of France, in 1305. Champagne and Navarre passed to the Capetian dynasty. King Stephen I of England, 1135–1154, was both a member of the House of Blois and the last Anglo-Norman King, being the grandson of William the Conqueror through his daughter Adela of Normandy. A branch of the family was established in Sancerre by Stephen I of Sancerre, a younger
Counts of Blois 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. Blois was important during the Hundred Years' War; Joan of Arc based herself there. The extent of the county varied over time. The northern portion, bordering on Normandy, was sometimes alienated as the County of