Alfonso VII of León and Castile
Sancho was the eldest son of King Alfonso VII of León and Castile and Berengaria of Barcelona. He was endowed with the "Kingdom of Nájera" in 1152, and according to Carolina Carl never appears in documents as "king of Nájera". His father's will partitioned the kingdom between his two sons: Sancho inherited the kingdoms of Castile and Toledo, and Ferdinand inherited León. The two brothers had just signed a treaty when Sancho suddenly died in the summer of 1158, being buried at Toledo.