Stefan was the eldest son of Stefan Nemanjić (r. 1196–1228), by his first wife Eudokia Angelina, daughter of Byzantine Emperor Alexios III Angelos (r. 1195–1203) and Euphrosyne Doukaina Kamaterina. He reportedly had two unnamed sisters, the first of whom married first the Albanian prince Dhimitër Progoni, and secondly the Greco-Albanian lord Gregorios Kamonas, while the second married the "sebastokrator" Alexander Asen, whom George Acropolites identifies as a son of Tsar Ivan Asen I of Bulgaria (r. 1189–96). It is uncertain if his mother was Maria or Helena, respectively the first and second wife of Ivan Asen I. Alexander was the father of Kaliman II of Bulgaria (r. 1256).