HRH Charles's 15-Great Grandfather. Lady Diana's 18-Great Grandfather. HRH Albert II's 16-Great Grandfather. HM Juan Carlos' 16-Great Grandfather. Philippe of Belgium's 16-Great Grandfather. Grand Duke Henri's 16-Great Grandfather. HM Margrethe II's 15-Great Grandfather. HM Beatrix's 15-Great Grandfather. HM Constantine II's 15-Great Grandfather. HM Carl XVI Gustaf's 15-Great Grandfather. HM Harald V's 15-Great Grandfather. HM Umberto II's 16-Great Grandfather.