Sancha, heiress of León

Sancha of León (born 1191 or 1192) was the eldest child and daughter of Alfonso IX of León by his first queen, Theresa of Portugal. She was raised at the court of the their father, but her younger sister Dulce and her brother Ferdinand were raised with their mother in Portugal after the annulment of their parents' marriage in 1195. Although in Castile it was customary for females to inherit, and Sancha's stepmother became queen, briefly, of Castile, in León female succession was barred, although her ancestor Urraca had been the first queen regnant of Western Europe.

After the death of Sancha's brother (1214), Alfonso IX named his second son, also Ferdinand, his heir, bestowing on him the title infante (1216). In 1217, with the support of the aristocracy, Alfonso granted his daughters Sancha and Dulce the villages of Portela de San Juan, Burgo de Ribadavia and Allariz, to be ruled by them until their deaths, after which they would revert to the Crown. In that same year, Ferdinand's mother, Berengaria, inherited the Kingdom of Castile, but ceded it to her son, who was proclaimed king at Valladolid on 2 July. With his heir out of the kingdom and ruling in another place, Alfonso attempted to make his eldest daughters his joint heirs. In the Treaty of Boronal concluded with Portugal in 1219, Alfonso expressly states that if he should die, Portugal should respect the agreement with his daughters.