After fighting a duel with Sir Thomas Canterbury at the successful defense of the city of Rennes against an English siege in 1356–57, du Guesclin was awarded a pension by the Dauphin (the future king Charles V) in December 1357. Appointed captain of Pontorson, he remained in the service of the French royal house of Valois. He fought in many battles (1359–63), being twice taken prisoner, and won a major victory at Cocherel in May 1364, defeating the troops of Charles II the Bad, king of Navarre, and taking prisoner Jean de Grailly (Grailly, Jean III de, Lord De Buch), captal de Buch, an ally of the English. He suffered a severe loss at Auray in September 1364, being taken prisoner after Charles, duc de Blois, whom he was supporting in the War of the Breton Succession, was killed. He was ransomed for 40,000 gold francs. In 1366 and in 1369 du Guesclin led the compagnies (bands of mercenaries) into Spain to aid Henry of Trastámara, bastard half brother of Peter I the Cruel, king of Castile, in his attempt to overthrow Peter. In 1370 Charles V recalled him from Spain to fight the English at Limoges. By 1373 he had given the French several major victories. He spent his remaining years on smaller expeditions against scattered English forces and mercenary bands and died besieging an enemy fortress.