I don't expect to ever have to use this but my kid brother knows one often-repeated-by-him thing about royal protocall, which is that if a Royal breaks wind in your presence, the correct thing to do is to say "Pardon me, Your Majesty." OK, I just can't do it,but my brother only tells that one in relation to the Queen- however a true courtier would substitute "Your Royal Highness" as required.