Isabella's claims to it were not secure, since her marriage to Ferdinand enraged her half-brother Henry IV of Castile and he withdrew his support for her being his heiress presumptive that had been codified in the Treaty of the Bulls of Guisando. Henry instead recognised Joanna of Castile, born during his marriage to Joanna of Portugal, but whose paternity was in doubt, since Henry was rumored to be impotent. When Henry died in 1474, Isabella asserted her claim to the throne, which was contested by thirteen-year-old Joanna. Joanna sought aid of her husband (who was also her uncle), Afonso V of Portugal, to claim the throne. This dispute between rival claimants led to the War of 1475–1479. Isabella called on the aid of Aragon, with her husband, the heir apparent, and his father, Juan II of Aragon providing it. Although Aragon provided support for Isabella's cause, Isabella's supporters had extracted concessions, Isabella was acknowledged as the sole heir to the crown of Castile. Juan II died in 1479, and Ferdinand succeeded to the throne in January 1479.