[@jordy0403][@Cultural Titan]

Most probable place I could see for the guy would be as Lethonel's personal servant/bodyguard.  The Kingsguard are already efficient protectors and vanguards, but Lethonel has the tendency to break into brutal fits of his disease-- this means that he might need to have a constant protector by his side through day and night (except bathroom, of course; that would be disturbing) like reminding the prince of his medicine and whatnot.  Of course, the Kingsguard would not really be suited to become a nanny on certain occasions.

This may also be useful when Lethonel goes on his researches around the kingdom.  At least, the Kingsguard have more responsibilities than becoming a personal caretaker of a certain royal.  

That would be my suggestion, but other than that, cheerios XD