Poss. HM George I's 12-Great Grandmother. Poss. U.S. President [A. JOHNSON]'s 14-Great Grandmother. Poss. PM Churchill's 17-Great Grandmother. Poss. Lady Diana's 18-Great Grandmother. Poss. PM Cameron's 19-Great Grandmother. Poss. Louis XVII's 16-Great Grandmother. Poss. Jamie's 20-Great Grandmother.