- Son of Alfonso IV of Aragon and his second wife Leonor of Castile, sister of Alfonso XI of Castile.
- Cousin of Pedro of Castile, who asked him for help to kill his half-brother Fadrique, Master of Santiago. [Pedro, ch. 20: 17]
- The princes Juan and Fernando of Aragon, cousins of Pedro of Castile through their mother, Queen Leonor, sided with the faction of Blanche of Bourbon and refused to serve the king unless he returned to his lawful wife and stopped bending to the influence of María de Padilla's brothers. [Pedro, ch. 17: 143-147]
- Pedro of Castile had Prince Juan killed in Bilbao, and immediately ordered the arrest of his mother and his wife, Doña Isabel de Lara. [Pedro, ch. 21: 56-70]
Joham