HRH Charles's 16-Great Grandfather. Lady Diana's 17-Great Grandfather. PM Cameron's 18-Great Grandfather. HRH Albert II's 16-Great Grandfather. HM Juan Carlos' 16-Great Grandfather. Philippe of Belgium's 17-Great Grandfather. HM Margrethe II's 16-Great Grandfather. HM Beatrix's 16-Great Grandfather. HM Constantine II's 16-Great Grandfather. HM Carl XVI Gustaf's 16-Great Grandfather. HM Harald V's 16-Great Grandfather. Ksr Wilhelm II's 14-Great Grandfather.