The reign of Juan, both as regent and afterwards as king, turns to a great extent on the acquisition of the kingdom of Navarre and the family quarrels which it kindled. In 1442 the mountain country on either side of the Pyrenees passed to the princely house of Aragon by the death of Blanche, wife of Juan, and previously the widow of King Martin. She had inherited Navarre from her father Charles III and by her will her patrimonial domains were to fall as an independent lordship to her eldest son Charles, prince of Viana. More as a matter of courtesy than a legal restriction the condition was added that, before assuming the government of the country, he should obtain the consent and approbation of his father. Juan seems at first to have made no difficulty to his son’s taking possession, so that Charles, while his father continued to bear the rank and title of king of Navarre, conducted the administration for several years as governor and ruler of his mother’s inheritance. But when the prince of Aragon contracted a second marriage with Juana Henriquez, daughter of a Castilian admiral of the blood royal, rivalries were awakened which soon assumed a malevolent character. According to the disposition of her husband, the new consort, an imperious, ambitious, and enterprising young lady, was to conduct the government of Navarre in conjunction with the prince of Viana. But the divided rule did not satisfy her proud spirit; as queen of Navarre she desired to be the only person to issue orders, and exhibited an arrogant demeanour towards her stepson. The disagreement soon passed into open hostility when the two conflicting parties of the Beaumonts and the Agramonts took the opportunity to fight out their ancient quarrels in sanguinary encounters, and the Castilians, exasperated at the interference of Aragon in their internal politics, fanned the flame. At the instigation of the Beaumonts, Charles laid claim to the chief power, and at the head of his adherents led an army into the field against the queen and the Agramonts. Juan of Aragon, dominated by his wife’s superior intelligence, took part against his son. A battle was fought at Aybar, when the prince of Viana was defeated and made prisoner (1452). Some months before, in the little town of Sos in Aragon, the queen had given birth to a son who, as Ferdinand the Catholic, was afterwards to attain to such great historical importance.