From Longman Dictionary of Contemporary EnglishYour/Her/His HighnessYour/Her/His HighnessHIGH POSITION OR RANKused to speak to or about a royal person such as a prince or princess → Highness
Examples from the Corpus
Your/Her/His Highness• But that's the deal, Your Highness.• No, Your Highness, you are, of course, welcome to stay.• Besides, I don't want anything from you, Your Highness. 