HRH Charles's 15-Great Grandmother. Lady Diana's 16-Great Grandmother. PM Cameron's 17-Great Grandmother. HRH Albert II's 15-Great Grandmother. HM Juan Carlos' 15-Great Grandmother. Philippe of Belgium's 16-Great Grandmother. Grand Duke Henri's 16-Great Grandmother. HM Margrethe II's 15-Great Grandmother. HM Beatrix's 15-Great Grandmother. HM Constantine II's 15-Great Grandmother. HM Carl XVI Gustaf's 15-Great Grandmother. HM Harald V's 15-Great Grandmother. Ksr Wilhelm II's 13-Great Grandmother.