[quote] by LAW Viscount Severn and Lady Louise are still a Prince and Princess with the rank of Royal Highness.
[quote] No. The Queen's prerogative of granting the latter, automatically cancelled out the former.
No, he was correct:
[quote] Louise is styled as "Lady Louise Windsor", although letters patent issued in 1917 (and still remaining in force today) assign a princely status and the style of Royal Highness to all male-line grandchildren of a monarch. Therefore, all else being equal, Louise would have been styled as Her Royal Highness Princess Louise of Wessex. However, when her parents married, the Queen, via a Buckingham Palace press release, announced that their children would be styled as the children of an earl, rather than as princes or princesses. Thus, court communications refer to her as Lady Louise Windsor.
Unless the law changes, she legally retains HRH status. But the queen has let it be known she will be styled "the Lady Louise Windsor," and so that it what she is addressed as, especially by the court communications. But legally she is HRH Princess louise of Wessex.
This is just like Camilla. Legally she is the wife of the Princess of Wales, so before the law she is HRH Camilla, the Princess of Wales, and that will remain in effect legally unless legislation is passed by Parliament to change it. But the queen has let it be known (according to Charles and Camila's wishes) that Camilla be styled "HRH Camilla, Duchess of Cornwall" and nothing more.
All titles theoretically flow from the sovereign while she/he is alive, but the second she dies Louise will be HRH the Princess Louise of Wessex (probably of Edinburgh by that time) and Camilla will become HM the Queen, unless Charles keeps the appellations (which he very well might do in Louise's case) or Parliament passes a law to the contrary.
So it's a weird situation. Legally the Duchess of Windsor was HRH Wallis, the Duchess of Windsor, because she was the wife of HRH the Duke of Windsor; but again, all titles flow from the sovereign, and both George VI and then Elizabeth after her insisted she be known only as Her Grace the Duchess of Windsor to spite her, and so that's what she was always called (except in private, where friends and servants called her "Your Royal Highness" and curtsied to her).