Secret pact of mutual defence Aragon and Navarre, 1363. Without ceasing to pretend war, a pact was agreed in Uncastillo on 25 August 1363; Pedro IV and Carlos II obliged themselves to mutual aid against the Castilians and the French. It was also stipulated that they would seek the marriage of Don Juan, Don Pedro's first-born, with Don Juana, sister of Don Carlos, giving her the same dowry that was given to Don Maria, wife of the same Don Pedro. The next day the two monarchs agreed on the way to divide the kingdom of Castile if they were to conquer it; they awarded to Navarre, Soria, clay, Biscay and the lands that were formerly part of the same kingdom, Burgos and all the land that is called Castile, Soria, clay, the land of Biscay, and the others that were formerly part of the royal domain of Navarre, leaving Murcia and Toledo for Aragon; that if the Count of Trastamara opposed this, both monarchs would help each other to force him. In addition, the king of Aragon promised the king of Navarre that if the latter managed to kill or to seize the man from Castile, to give him Jaca with its belongings, both in the mountains and in the canal, Sos, Uncastillo and Ejea; these towns of Aragon were handed over as ages to the king of Navarre for the fulfilment of the treaty, with the Count of Ribagorza as guarantor (Yanguas: "Dictionary...").