It would be almost impossible for the madness of royalty to go unwatched, given how closely watched they are in general. Whatever a royal person does he has a multitude of eyes upon it. In some cultures, royals get no privacy whatsoever, not even to take a shit in peace. There is someone with you at all times.
That would make me mad pretty darn quickly, I can tell you. With never a moment on my own to collect my thoughts, I would be a raving lunatic in a matter of days.
And maybe that explains why there has been so much madness in the kingdoms around the world – they were watched to the point of madness and then watched through madness and so on and so on.