my comment was based on a movie https://en.wikipedia.org/wiki/The_Exception based on https://en.wikipedia.org/wiki/The_Kaiser%27s_Last_Kiss Of course any monarchy would've recognized the Nazis so maybe the monarchs would have been as figureheads only. Reading more, looks like the book might not be 100% accurate. For example, Himmler did not meet the exiled last Kaiser but Goring did.