Royal Highness
From Longman Dictionary of Contemporary EnglishRoyal HighnessˌRoyal ˈHighness noun [countable] → your/his/her Royal HighnessExamples from the CorpusRoyal Highness• Her Royal Highness went round the room meeting many of those who had supported this Gala evening.• Her Royal Highness who was looking radiant, assured everybody that she would be back on skis at next year's Championships.• His Royal Highness was not available for comment, except in dire necessity.