HM George I's 11-Great Grandfather. HRE Charles VI's 12-Great Grandfather. Poss. Lady Diana's 20-Great Grandfather. PM Cameron's 20-Great Grandfather. HRH Albert II's 20-Great Grandfather. HM Margrethe II's 18-Great Grandfather. Boris Johnson's 19-Great Grandfather. `Red Baron' Richthofen's 16-Great Grandfather.