His mother died first on 18 November 1313, followed by Infantes John and Peter during a military campaign against Granada in 1319 at the Disaster of the Vega, which left Dowager Queen María as the only regent until her death on 1 July 1321.

[citation needed] Alfonso inherited the throne at a time of instability within the region, decline in populations, reductions in the royal treasury and increasingly ambitious regents caused numerous problems during his young reign.

[4] After the death of the Infantes John and Peter in 1319, Philip (son of Sancho IV and María de Molina, thus brother of Infante Peter), Juan Manuel (the king's second-degree uncle by virtue of being Ferdinand III's grandson) and Juan the One-eyed (his second-degree uncle, son of John of Castile who died in 1319) split the kingdom among themselves according to their aspirations for regency, even as it was being looted by Moors and the rebellious nobility.

[8] He managed to extend the limits of his kingdom to the Strait of Gibraltar after the important victory at the Battle of Río Salado against the Marinid dynasty in 1340 and the conquest of Algeciras in 1344.

The first two names he earned by the ferocity with which he repressed the disorders caused by the nobles during his long minority; the third by his victory in the Battle of Río Salado over the last formidable Marinid invasion of the Iberian Peninsula in 1340.

[12] Out of respect, Alfonso's rival Yusuf I of Granada ordered his army and his commanders in the border regions not to attack the Castilian procession as it traveled with the king's body to Seville.