Another *hint hint* Diana has no royal blood line. She was a commoner and was only married into the royal family and actually never was a true princess or should have been given the title like the media always gave her.
Found this tidbit: Diana, Princess of Wales (Diana Frances Mountbatten-Windsor, née Spencer) (1 July 1961–31 August 1997) was the first wife of HRH The Prince Charles, Prince of Wales. From her marriage in 1981 to her divorce in 1996 she was styled Her Royal Highness The Princess of Wales. She was almost always called Princess Diana by the media despite never having had the right to that title, as it would imply that she was a princess by birthright rather than by marriage.