Now one of Edward's strongest supporters, he accompanied the king on a campaign to Scotland in 1314, when several other nobles refused. He was killed at the Battle of Bannockburn on 24 June, under somewhat unclear circumstances. Gloucester was the most prominent of the casualties of the battle, which ended in a humiliating defeat for England. As he had no issue, his death marked the end of the prominent de Clare family. His estates were divided between his three sisters, one of whom was married to the king's new favourite, Hugh Despenser the younger. Despenser's ruthless expansion of the de Clare lordship of Glamorgan in Wales led directly to the troubles of Edward II's later reign, including a rebellion in the Welsh Marches, the defeat of the Earl of Lancaster at the Battle of Boroughbridge, and eventually the deposition of the king by Roger Mortimer and Queen Isabella in 1326.