HM George I's 9-Great Uncle. U.S. President [McKINLEY]'s 14-Great Grandfather. HRH Charles's 16-Great Grandfather. PM Churchill's 15-Great Grandfather. Lady Diana's 16-Great Grandfather. PM Cameron's 17-Great Grandfather. HRH Albert II's 17-Great Grandfather. Poss. Jamie's 16-Great Grandfather.