The arms of King Edward IV when Duke of York emphasise his descent from Lionel of Antwerp, 1st Duke of Clarence (1338–1368), third son of King Edward III (on which basis the House of York claimed the throne), who married Elizabeth de Burgh, 4th Countess of Ulster (1332–1363). Their daughter Philippa de Burgh married Edmund Mortimer, 3rd Earl of March, whose son Roger de Mortimer, 4th Earl of March, was the great-grandfather of King Edward IV, whose illegitimate son was Arthur Plantagenet, 1st Viscount Lisle, KG, (died 1542), whose daughter Frances Plantagenet was the wife of Thomas Monk of Potheridge, the Duke of Albemarle's great-grandfather.