Ferdinand of León_

Ferdinand was the eldest son and heir apparent of Alfonso IX of León by his first wife, Theresa, daughter of Sancho I of Portugal. He predeceased his father, unmarried and without issue at the age of about 22. According to the historian Lucas of Tuy, who called Ferdinand "an extremely handsome youth", the "king of León grieved profoundly for his death" and had him buried in the cathedral of Santiago de Compostela, where his grandfather and namesake, Ferdinand II, was buried. The new heir apparent then became another Ferdinand, Alfonso's first son by his second wife, Berengaria of Castile.