During the wars of his elder brother Henry V in France, Clarence fought in both the Siege of Caen and the Siege of Rouen (29 July 1418 – 19 January 1419), where he commanded the besieging force. After Henry had negotiated the Treaty of Troyes, in which he became heir to the French throne, the king returned to England with his new wife Catherine. The Dauphin, the disinherited former heir, refused to accept the situation and organised continuing resistance, aided by a Scottish army led by John Stewart, Earl of Buchan.