Warner Bros., DC Comics and Superman co-creator Jerry Siegel (technically, his estate) have been locked in a custody battle for Superman for some time now, and the latest stage in the case has gone Warner Bros.’ way – but the continuing suit could force Warners to put a Superman film in development by 2011 in order to hold onto the rights.

This is a bit dry, but stick with us. The contention of Siegel’s heirs was that DC Comics made a “sweetheart deal” with Warners, giving the latter the rights to film Superman Returns at a fraction of their market value. If proved, this would have allowed the Siegel estate to share in the movie profits as well as income from the comics.

U.S. Judge District Court Judge Stephen G. Larson rejected that argument on Wednesday. The Siegels’ attorney, Marc Toberoff, however, claimed that the judgment also noted that it was “inequitable” that there was no reversion clause in the Warners/DC agreement, which would allow the Superman film rights to revert back to DC (and the Siegels) if Warners did nothing with them for a certain length of time.

The Court ruled that if Warners did not put a Superman film in development by 2011, the Siegels could sue to recover damages as a result of the non-reversion. Given that part of the copyright in any case reverts back to the Siegel estate and that of co-creator Joe Shuster in 2013 anyway, there is now a definite timetable within which Warners will need to get a film moving if they’re to make another Man of Steel film.

So if in the next 18 months or so you hear word of a new Superman film in production, don’t say I didn’t warn you.