HRH Charles's 16-Great Grandmother. Poss. Lady Diana's 15-Great Grandmother. HM Juan Carlos' 16-Great Grandmother. HM Margrethe II's 15-Great Grandmother. HM Beatrix's 12-Great Grandmother. Wm. von Bismarck's 11-Great Grandmother. `Red Baron' Richthofen's 12-Great Grandmother.