Courtesy Title I hesitate for a moment before entering the fray but wish to say that I entirely agree with an interpretation which asserts the binding nature of letters patent and the non optional status of the existence of the style HRH and title princess if not their use The point I raise relates to the amendments I have just made namely that the person in question can not be properly described as The Lady Louise as the definite article The is for use in substantive titles of the peerage As this title is a courtesy title there should be no such article and it should read Lady Louise Windsor I must say also that I still don t quite get how her surname can be Mountbatten Windsor but her title a courtesy title for the daughter of an earl can use an alternative surname