Good question, PrinceS; I remember to have seen a copy of the wedding certificate of Charles and Camilla, where he is officially referred as "His Royal Highness Prince Charles Philip Arthur George THE PRINCE OF WALES", and his father is referred as "His Royal Highness the Prince Philip".
http://i39.tinypic.com/bvkte.jpg
I guess in wedding certificates are used the complete and official identification state of a person, so I guess these are the identification states of Charles and Philip; so I guess that Prince Michael's identification state is "His Royal Highness Prince Michael George Charles Franklin".