HRH Charles's 17-Great Aunt. Lady Diana's 18-Great Aunt. HM Juan Carlos' 18-Great Grandmother. Philippe of Belgium's 18-Great Grandmother. Grand Duke Henri's 18-Great Grandmother. HM Margrethe II's 18-Great Grandmother. HM Beatrix's 14-Great Grandmother. HM Constantine II's 14-Great Grandmother. HM Carl XVI Gustaf's 14-Great Grandmother. `Red Baron' Richthofen's 12-Great Grandmother.