The 1909 "The Count of Luxemburg" was by a composer whose best known and most successful operetta was what?
The Count of Luxemburg (1957 film):  It is based on the 1909 operetta "The Count of Luxemburg" by Franz Lehár. Franz Lehár: Franz Lehár (Hungarian: "Lehár Ferenc" ; 30 April 1870 – 24 October 1948) was an Austro-Hungarian composer.
i don't know