He was the son and heir of María II Díaz de Haro, from whom he inherited the Lordship of Biscay, and her husband the infante John of Castile.

This marriage produced the following children: The chronicle of the reign of Alfonso XI of Castile describes the minority of the young king as a time of violence and social tension, when knights and powerful lords robbed and oppressed those weaker than them.

[2] In 1325, the fourteen year old king announced his intention to rule in his own right, without the aid of the regents who had exploited their time in control.

Juan el Tuerto was lured to Toro with the prospect of a pardon and reconciliation with King Alfonso.

On 1 November 1326, the king ordered the murder of el Tuerto and two of his knights, then summoned the nobles to the square to hear an account of the infante's treasonable conduct.