HRH Charles's 12-Great Grandmother. PM Cameron's 14-Great Grandmother. HRH Albert II's 15-Great Grandmother. HM Juan Carlos' 12-Great Grandmother. Philippe of Belgium's 13-Great Grandmother. HM Manuel II's 12-Great Grandmother. Grand Duke Henri's 13-Great Grandmother. HM Margrethe II's 12-Great Grandmother. HM Beatrix's 12-Great Grandmother. HM Constantine II's 12-Great Grandmother. HM Carl XVI Gustaf's 12-Great Grandmother. HM Harald V's 12-Great Grandmother. Ksr Wilhelm II's 10-Great Grandmother. HM Umberto II's 14-Great Grandmother. Boris Johnson's 15-Great Grandmother.