HRH Charles's 15-Great Grandfather. Lady Diana's 16-Great Uncle. PM Cameron's 17-Great Uncle. HRH Albert II's 15-Great Uncle. HM Juan Carlos' 15-Great Uncle. 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. Ksr Wilhelm II's 13-Great Grandfather.