"The Screen Guild Theater" broadcast a 30 minute radio adaptation of the movie on February 14, 1944 with Errol Flynn, Alexis Smith and Ward Bond reprising their film roles.
Errol Flynn did all of his own boxing stunts in the film, and although production was shut down for a time after Flynn suffered a mild heart attack, he came back and finished the picture without ever using a double.
According to "Variety," the real Corbett was "self-effacing" and had a "quiet personality.," which is at odds with the brash extrovert that is pictured in the film.
Director Walsh originally wanted Barry Fitzgerald for Corbett's father and suggested Ann Sheridan and Rita Hayworth for the romantic lead.
During the filming of Gentleman Jim, Errol Flynn suffered a mild heart attack. His weak heart kept him from serving in the Armed Forces during World War II.
Former Junior Welterweight champion Mushy Callahan not only trained Flynn for the film's fight sequences, his feet doubled for the actor in the shots that showed off his famous footwork.
Mike Mazurki and Ed 'Strangler' Lewis started their careers as professional wrestlers.
Soon after completing "Gentleman Jim," Flynn became embroiled in an infamous rape trial. During screenings of "Gentleman Jim," his closing line of "I'm no gentleman" was met with laughter and derision. The line was cut from the conclusion of the 1944 radio broadcast.
Sullivan reportedly did not like Corbett, and although the film shows Sullivan presenting his championship belt to him, in real life the belt had been hocked by the champion years before.
The 2/14/44 Screen Guild radio broadcast of "Gentleman Jim" reunited Flynn, Smith, and Bond, but Grant Withers replaced Jack Carson as Walter Lowrie.
The press announced Phil Silvers for "Gentleman Jim," but he was never signed. Presumably he would played the Jack Carson role.
The real Sullivan had fought Corbett had fought prior to their world championship bout at San Francisco's Olympic Club some years before.
The sailing ship used during the dock-side fight was the same one used during filming of The Sea Hawk.