Father and son eventually reconciled to assist the king's aim of acquiring the neighbouring Duchy of Austria, where the last Babenberg duke, Frederick II had been killed in the 1246 Battle of the Leitha River. King Wenceslaus had initially attempted to acquire Austria by marrying his heir, Vladislaus, to the last duke's niece Gertrude of Babenberg. That marriage came to an end after half a year with Vladislaus's death in January 1247, and in 1248 Gertrude married the Zähringen margrave Herman VI of Baden. Herman, rejected by the Austrian nobility, could not establish his rule. Wenceslaus used this as pretext to invade Austria when Herman died in 1250 — according to some sources, the estates called upon him to restore order.