Ferdinand was born in the city of Seville on 6 December 1285 as the second child and eldest son of King Sancho IV of Castile and his wife María de Molina.
He was baptized at Seville Cathedral by Archbishop Raimundo de Losana and was immediately proclaimed heir to the Crown and received the homage of the nobles of the kingdom.

King Sancho IV entrusted to Fernán Pérez Ponce de León the raising of his newborn son, since he had been first majordomo of King Alfonso X. The prince and his tutor left for the city of Zamora, where the family of Fernán Pérez resided.
Likewise the King appointed Isidro González and Alfonso Godínez as Chancellors of the prince, while appointing Samuel de Belorado almojarife (Treasurer) of the prince.
Fernán Pérez Ponce de León and his wife, Urraca Gutiérrez de Meneses, had a significant influence on Ferdinand's character, and he would show them, as a King, a profound gratitude.

Already in his infancy the question of his marriage was raised, being the desire of Sancho IV to choose a princess from Kingdoms of France or Portugal.
In the agreement signed by Sancho IV and King Denis of Portugal in September 1291, was established the betrothal between Ferdinand and the Infanta Constance, daughter of the Portuguese sovereign.
Nevertheless, in spite of the commitment contracted with the Portuguese monarch, in 1294, Sancho IV thought about the possibility of marrying his son with Margaret or Blanche, daughters of King Philip IV of France.
The death of Sancho IV a year later put an end to the negotiations with the French court.
Ferdinand was born in the city of Seville on 6 December 1285 as the second child and eldest son of King Sancho IV of Castile and his wife María de Molina. He was baptized at Seville Cathedral by Archbishop Raimundo de Losana and was immediately proclaimed heir to the Crown and received the homage of the nobles of the kingdom.
King Sancho IV entrusted to Fernán Pérez Ponce de León the raising of his newborn son, since he had been first majordomo of King Alfonso X. The prince and his tutor left for the city of Zamora, where the family of Fernán Pérez resided. Likewise the King appointed Isidro González and Alfonso Godínez as Chancellors of the prince, while appointing Samuel de Belorado almojarife (Treasurer) of the prince. Fernán Pérez Ponce de León and his wife, Urraca Gutiérrez de Meneses, had a significant influence on Ferdinand's character, and he would show them, as a King, a profound gratitude.
Already in his infancy the question of his marriage was raised, being the desire of Sancho IV to choose a princess from Kingdoms of France or Portugal. In the agreement signed by Sancho IV and King Denis of Portugal in September 1291, was established the betrothal between Ferdinand and the Infanta Constance, daughter of the Portuguese sovereign. Nevertheless, in spite of the commitment contracted with the Portuguese monarch, in 1294, Sancho IV thought about the possibility of marrying his son with Margaret or Blanche, daughters of King Philip IV of France. The death of Sancho IV a year later put an end to the negotiations with the French court.
Ferdinand IV of Castile