HRH Charles's 16-Great Half-Aunt. Poss. Lady Diana's 16-Great Grandmother. HM Juan Carlos' 16-Great Half-Aunt. HM Margrethe II's 17-Great Half-Aunt. HM Beatrix's 15-Great Grandmother. Wm. von Bismarck's 12-Great Grandmother. `Red Baron' Richthofen's 13-Great Grandmother.