Henry agreed to betroth his son John to Elizabeth of Celje, the daughter of Count Ulrich II, a project that ulimatively was not realized.

Elisabeth was betrothed to Matthias Corvinus, future king of Hungary, in a futile attempt to reconcile the houses of Celje and Hunyadi.

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.

Nevertheless, he went on to occupy and plunder the Ortenburg lands, until he was finally defeated by the Habsburg forces of Emperor Frederick III in 1460, under the command of the Bohemian condottiere Jan Vitovec who had previously served the Counts of Celje.