Soon afterwards the cause of Pedro of Castille became hopeless. His illegitimate brother Henry of Trastamara, aided by the Ceremonious tyrant of Aragon, advanced into Spain with an army and besieged the castle of Burgos, which had been occupied by Jayme and his troops. The King of Majorca made a gallant defence, but at last he was obliged to surrender. His odious uncle of Aragon tried to get his unfortunate nephew into his clutches again; but love was ready to make greater sacrifices than hatred. The Queen of Naples ransomed her husband for sixty thousand _doblas_.
In March 1369 Jayme was safe in the territory of the Count of Foix. Thence he proceeded to Avignon and began to collect troops, intending to invade Roussillon, which had been unjustly occupied by the usurper. His whole heart was devoted to what he considered the duty of avenging his father’s death. He looked upon his uncle Pedro as a usurper and murderer, and his hatred for the Ceremonious one was intense. Friends represented to him that he should be satisfied with the kingdom of Naples and a devoted wife. But he answered that he was bound to avenge his father. When it was represented to him that attacks with inadequate forces on so powerful an enemy could only lead to his own destruction, he replied that he could not die in a better cause.
The Companies were then overrunning France. Young Jayme enlisted Englishmen, Frenchmen, and Provençals, the funds being supplied by his Queen. He advanced with his little army to Narbonne, and thence to Toulouse. His beloved sister Isabel, who had become the wife of the Marquis of Monserrat, joined her brother when he invaded his own territory of Roussillon. The town of Perpignan was too strong for attack, and the Ceremonious one was making great preparations for the defence of Catalonia. His army was assembled in the Ampurdan to oppose an entry by the Pass of Panizas. The young King of Majorca therefore crossed the Pyrenees, entering by the Puig-cerdan Pass, and occupied the county of Urgel. His uncle of Aragon resorted to a way more in accordance with his nature than a fair fight. He poisoned his nephew. The secret crime was perpetrated at Valderan, near Urgel. Jayme died in his sister’s arms, rendering up a life which had been devoted to the memory of his unhappy father. It was in January 1375 that the last King of Majorca and King Consort of Naples expired within his own rightful dominions of Cerdaña. His body was buried in the Franciscan monastery of Soria. His sister Isabel returned into Gascony, and died in 1379, the last of her race.