Apparently (at least according to wikipedia), King Matthias Corvinus of Hungary wanted to have HRE Friedrich III acknowledge Matthias' bastard son, Janos, as Prince Royal of Hungary in exchange for Matthias' renouncing his claims to all/parts of the Austrian hereditary archduchy. However, Matthias died before peace-talks were finalized, and between the nobles Matthias had crushed and the dowager Queen Beatrice d'Aragon, they swiftly removed Janos from the halls of power by forcing him to relinquish most of the estates his father had bestowed on him.
Now, Matthias had also toyed with the idea, at some point, of marrying his son to Bianca Maria Sforza (she who became Holy Roman Empress), however, Queen Beatrice had once again blocked this path, and Janos was married off to a girl from the Frankopan family instead.
What if Matthias had lived to see Friedrich III acknowledge Janos as Prince Royal? Would Friedrich have done this? And even if Friedrich did recognize the boy, would it carry any weight? After all, Friedrich recognized Perkin Warbeck (I think) and it didn't better his chances at becoming king of England.