HRH Charles's 15-Great Uncle. Lady Diana's 15-Great Grandfather. HM Juan Carlos' 15-Great Uncle. Philippe of Belgium's 16-Great Uncle. Grand Duke Henri's 16-Great Uncle. HM Margrethe II's 15-Great Uncle. `Red Baron' Richthofen's 15-Great Grandfather. HRH Catharina-Amalia's 14-Great Grandfather.