"Stephen V (Hungarian: V. István, Croatian: Stjepan V., Slovak: Štefan V; before 18 October 1239 – 6 August 1272, Csepel Island) was King of Hungary and Croatia ...
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between 1270 and 1272, and Duke of Styria from 1258 to 1260. He was the oldest son of King Béla IV and Maria Laskarina. King Béla had his son crowned king at the age of six and appointed him Duke of Slavonia. Still a child, Stephen married Elizabeth, a daughter of a chieftain of the Cumans whom his father settled in the Great Hungarian Plain.
King Béla appointed Stephen Duke of Transylvania in 1257 and Duke of Styria in 1258. The local noblemen in Styria, which had been annexed four years before, opposed his rule. Assisted by King Ottokar II of Bohemia, they rebelled and expelled Stephen´s troops from most parts of Styria. After Ottokar II routed the united army of Stephen and his father in the Battle of Kressenbrunn on 12 July 1260, Stephen left Styria and returned to Transylvania." - (en.wikipedia.org 03.10.2020)
