Henry IV of Castile sibling Alfonso
Death
However, in 1468, at the age of only 14, Alfonso died, most likely from the plague (although poison and slit throat have been suggested). His will left his crown to his sister, Isabella, who was asked to take her brother's place as the champion of the rebels. Shortly thereafter at the negotiation of Toros de Guisando, in which she and her allies received most of what they desired, Henry agreed to exclude Joanna la Beltraneja from the succession, and to recognize Isabella as his official heir. Though Henry continued to resist this decision when possible, his actions were ineffective, and he remained at peace with Isabella for the rest of his reign. Isabella became Castile's next monarch when he died in 1474.
After the death of the king, war broke out in Castile. Joanna was supported by Portugal, while the eventual winner, Henry's half-sister Isabella I of Castile, had the support of Aragon. France initially supported Joanna, yet in 1476, after losing the Battle of Toro, France refused to help Joanna further and in 1478 signed a peace treaty with Isabella.
brother or sister kin