owes his sobriquet the Cruel to his ready use of murder and execution to eliminate his political opponents, including, reportedly, several of his ambitious half brothers. His principal conflict was with his older half brother, Henry of Trastamara, who also claimed the throne. Henry enlisted the aid of King Charles V of France, who in 1365 sent troops through Spain under the command of Bertrand Du Guesclin. Overthrown, Peter left the country and requested aid from Edward III of England, at that time engaged in fighting the Hundred Years' War with France; Edward sent an army commanded by his son Edward, prince of Wales, known as the Black Prince. The forces of Peter and Edward defeated those of Henry, the French, and other allies at the Battle of Nájera in 1367, and Henry fled to France. Political differences between Peter and Edward resulted in the latter's withdrawal from Spain with his army. Henry then hastened back and with Du Guesclin's help engaged Peter and his supporters in a civil war. Peter was defeated and killed at Campo de Montiel in 1369; Henry assumed the throne as King Henry II.