The divine right of kings was a cynical move on the part of a Roman emperor. Diocletian, I think. To secure his position and make people listen to and obey him. But it's been taken as read from there until the present, in one form or another.
Harry as been brought up to rule. Should anything have happened to William, until Kate got pregnant, it would eventually be him on the throne. His family tree allegedly contains such figures as Odin and Mohammed. Those factors will breed someone pretty entitled indeed. While I understand that, I still think it's a stupid move. Maybe he needs a handler to remind him of such things. Or maybe he has one that he ignores.