I wanna put it out there--royalty have a bad habit of fucking around. Kings, Queens, Princes, Princesses; usually, the unwanted kids become commoners or are traded to other nobility.
Sometimes they become scapegoats, or assassins, or sometimes... Just sometimes, rarely?
They get successfully swapped out for a doppelganger at birth. Some real "we're back writing 1300s fiction" shit, but it has happened before.