Complex sentence: Darryl F. Zanuck was also worried about Lang's anti-Nazi enthusiasm and banned him from the editing room, but Lang and his associate Gene Fowler, Jr. edited the film without Zanuck's approval.
Split into simpler sentences: Darryl F. Zanuck was also worried about Lang's anti-Nazi enthusiasm and banned him from the editing room. However Lang and his associate Gene Fowler, Jr. secretly edited the film without Zanuck's approval.