Philip became duke of Burgundy and count of Flanders, Artois and Franche-Comté upon the assassination of John the Fearless, his father, in 1419. Philip accused Charles, the Dauphin of France and Philip's brother-in-law, of planning the murder, which took place during a meeting between John and Charles at Montereau. Because of this, he continued to prosecute the Armagnac–Burgundian Civil War, which in turn became entangled in the larger Hundred Years' War. In 1420, Philip allied himself with Henry V of England under the Treaty of Troyes. In 1423, the marriage of Philip's sister Anne to John, Duke of Bedford, regent for Henry VI of England, strengthened the English alliance.