HRH Charles's 17-Great Grandmother. Poss. Lady Diana's 16-Great Grandmother. HM Juan Carlos' 17-Great Grandmother. HM Margrethe II's 16-Great Grandmother. HM Beatrix's 13-Great Grandmother. Wm. von Bismarck's 12-Great Grandmother. `Red Baron' Richthofen's 13-Great Grandmother.