Pedro had problems. As the king of Castile since 1350, he had endeavored to conquer the region of Valencia from his neighbor, Pere IV of Aragon (r. 1336–1387). In waging this War of the Two Pedros against Aragon, Pedro had concluded an alliance with England and won the hostility of France. With these international political developments, Pedro found that Castile had become a new theater of operations in the Hundred Years’ War. Meanwhile, Pere IV had given financial and political support to a claimant to the Castilian throne, Pedro's half-brother Fadrique. A paranoid man, perhaps rightly so, Pedro worked to secure his place on the throne throughout his reign by destroying his enemies wherever he found them. During his nineteen years on the throne, Pedro was rumored to have discovered among his enemies some leading nobles of the realm, royal advisors, his half-brother, an archbishop, and even the French princess who was his wife; he had them all murdered. In this atmosphere of hostility and suspicion, many noblemen rose against Pedro, finding an alternative claimant to the throne in another of his half-brothers, Enrique de Trastámara. In 1366, the realm had erupted into full-blown civil war. It seems that Pedro's violent actions had returned violence upon him.

Indeed, Pedro's problems were about to get much worse. In 1369 the king found himself besieged by Enrique's army in the castle of Montiel in south-central Castile. Desperately, Pedro contacted a French mercenary in Enrique's army, a knight named Bertrand du Guesclin, and offered him a handsome payment and future lordship if the French knight would help him to escape his predicament. Bertrand, ever the opportunist, went to Enrique and asked him to beat his half-brother's offer. Enrique was all too happy to participate and Bertrand agreed to betray Pedro. On the evening of March 23, 1369, King Pedro snuck out of the castle of Montiel, and Bertrand led the monarch to his tent in the besiegers’ camp. Bertrand stepped out, ostensibly to prepare horses for Pedro's flight, and in stepped Enrique de Trastámara.