Stephen succeeded his father, who died on 3 May 1270, without difficulties, but his sister Anna and his father's closest advisors fled to the Kingdom of Bohemia.
István menggantikan ayahandanya, yang meninggal pada tanggal 3 Mei 1270 tanpa kesulitan, namun adindanya, Anna dan penasihat terdekat ayahandanya melarikan diri ke Kerajaan Bohemia.