Henry de Trastámara, with the Black Prince gone from Castile, leads a second invasion with French help.

Bertrand du Guesclin had won renown in May, 1364, for winning the battle of Cocherel in Normandy against the opponents of Charles V. Except for this victory, he is unsuccessful in pitched battles, having lost at Auray in 1364 and Nájera in 1367; although eventually celebrated as a symbol of chivalry, he is most successful at such unchivalrous pursuits as brigandage and guerrilla warfare Respected by—and thus able to control—the fierce warriors who are the scourge of the countryside when undisciplined, du Guesclin leads such troops in successfully installing the pro-French Trastamara on the throne of Castile (and León) as Henry II after he defeats his half-brother Peter of Castile and León at Montiel, and murders him on March 23, 1369.

The new Castilian regime will provide naval support to French campaigns against Aquitaine and England.