HRH Charles's 16-Great Grandfather. Lady Diana's 15-Great Grandfather. PM Cameron's 17-Great Uncle. HRH Albert II's 15-Great Grandfather. HM Juan Carlos' 15-Great Uncle. Philippe of Belgium's 16-Great Grandfather. Grand Duke Henri's 16-Great Grandfather. HM Margrethe II's 16-Great Grandfather. HM Beatrix's 14-Great Grandfather. HM Constantine II's 16-Great Grandfather. HM Harald V's 16-Great Grandfather.