Complex sentence: Although it was not officially acknowledged the film is based on the 1902 novel Brewster's Millions by George Barr McCutcheon based on which at least six films have earlier been made besides a Broadway play.
Split into simpler sentences: Although it was not officially acknowledged the film is based on the 1902 novel Brewster's Millions by George Barr McCutcheon. At least six films have earlier also been made based on the novel, besides a Broadway play.