- In 1356, Francesc del Perelló, an Aragonese captain, was in the port of Sanlúcar de Barrameda with a fleet of ten Aragonese galleys ready to be sent to the King of France to assist him against the English. While there, the captain seized two Genoese ships because Aragon was at war with Genoa. Pedro of Castile forbid him to do so, since Sanlúcar de Barrameda was Castilian territory, and threatened to imprison all Catalans in his kingdom. The captain disregarded the royal order and sold the Genoese ships.
- Pedro of Castile, enraged by this act of disrespsect, sought revenge out of proportion, in Fernão Lopes's words. He sent word to the King of Aragon demanding that Francesc del Perelló be returned to Castile to answer for his act of disrespect. Furthermore, Pedro Moñiz de Godoy, a trusted vassal of Pere IV of Aragon, but hated by the King of Castile, should be divested of privileges granted to him by the King of Aragon otherwise hostilities between the two countries would commence. Pere IV sought a compromise but to no avail. Seeing that Pedro was intent on war, Aragon immediately initiated preparations.
- Pere IV of Aragon sends word to dissidents against the King of Castile including the Count of Trastámara, Pedro's half-brother who was in France at the service of Jean II against the English, and gives him the means to maintain a force of 800 horsemen. In retaliation, Pedro invades Aragon and seizes a few castles.
- Pope Innocent VI sent his legate, Cardinal Guillaume de la Jugie, who managed to negotiate a truce, but Pedro took advantage of it and seized the Aragonese town of Tarazona, leaving it defended with a large force, including Englishmen.
- Unable to establish an enduring truce, the Pope legate decreed a period of peace to last a full year. Pedro of Castile, however, immediately ordered new ships to be built in order to attack Aragon as soon as the year ended.
- In 1361, Pedro of Castile invaded Aragon. Guy de Boulogne, the Papal legate, intervened to put an end to hostilities. [Pedro, ch. 32: 38-65]
Chronicle entries in which War between Castile and Aragon appears:
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