Is it possible that you are thinking of a character from the bible...? No, the one I have in mind actually DID find the boy-king (to be).
There are also examples from Greek sagas, but in anyone I can think of the character at least met the boy-king (e.g. Odysseus / Ulisses who found a way to discover the young Achillieus who had been disguised as a girl hidden among many other girls).
It would be helpful to have a little more hints Nick.