I thought Prince Philip was a prince in his own right?!? Wasn't his title at one time Philip, Prince of Greece and Denmark, or something similar to that?
Prince Philip was indeed Prince in his own right - a Prince of Greece and Denmark.
However, before his marriage to princess Elizabeth, he renounced all his Greek styles and titles. George VI created Philip a Royal Highness and the Duke of Edinburgh - but
not Prince of the United Kingdom. So, technically from 1947 to 1957, Philip's title was His Royal Highness The Duke of Edinburgh (without the Prince, although he was still known as such). In 1957, Queen Elizabeth granted Philip the title of Prince of the United Kingdom of Great Britain and Northern Ireland and since then he has been
His Royal Highness The Prince Philip, Duke of Edinburgh
Of other spouses of British Queens Regnant, none was created a Prince of the United Kingdom (or its predecessor states) in their own right. Prince Albert (Queen Victoria's husband) was made The Prince Consort (the only consort in British history to have had the official title), but not a Prince of the United Kingdom.
The closest example to Prince Philip's situation was probably that of
Princess Alice, Duchess of Gloucester. When Prince Henry, Duke of Gloucester (Alice's husband) died, she was to be known as The Dowager Duchess of Gloucester to avoid confusion with the new Duchess of Gloucester (Birgitte, the wife of Prince Richard); however Alice was known to intensely dislike the style, so she ask the queen's permission to be known as
Princess Alice, Duchess of Gloucester. Alice's sister -in-law, Marina, Duchess of Kent, was also known (after her husband's death and son's marriage) as Princess Marina, Duchess of Kent - instead of the Dowager Duchess of Kent. However, Marina was Princess by birth (of Greece and Denmark), whereas Alice had been merely a Lady. Alice's title of Princess was a personal courtesy from the Queen - although no formal letters patent were ever issued to recognise that style. Nevertheless, from 1974 and until her death in 2004, Alice's full style and title was Her Royal Highness Princess Alice, Duchess of Gloucester; in other words, she was styled and titled as a Princess by birth, not by marriage.