noun
His / Her / Your Royal Highness a title of respect used when talking to or about a member of the royal family :
Their Royal Highnesses, the Duke and Duchess of Kent
noun
His / Her / Your Royal Highness a title of respect used when talking to or about a member of the royal family :
Their Royal Highnesses, the Duke and Duchess of Kent
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005