After his release upon his father's death in 1454, John took up government in Gorizia. In November 1456, he was part of the entourage of Ulrich II of Celje and Ladislaus the Posthumous that was supposed to take over Belgrade Fortress from Hunyadi troops that had just repelled an Ottoman siege. Ulrich was assassinated by the Hunyadis, and John went on to claim the extinct Ortenburg estates in the Duchy of Carinthia (around Millstatt and Spittal an der Drau), which were bordering the Gorizia palatine county in the upper Drava valley.