Two classic DC film heroes, Christopher Reeve’s Superman and Michael Keaton’s Batman, are popularly theorized to share a universe, and an issue of Superman ’78 hints that this theory may be true. Superman is a pop culture icon, whose popularity goes far beyond his classic comic book appearances. In 1978 (forty years after his comic debut), the breathtaking talents of Christopher Reeve, Richard Donner, and many others brought him and his supporting characters to life in a now-iconic blockbuster film. Over a decade later, Batman returned to theaters for the first time in decades in Tim Burton’s classic film, starring Michael Keaton as the Dark Knight. Both series’ have recently been revived in the ongoing Superman ’78 and Batman ’89 comics, and the former implies that the two are part of the same continuity.

The classic Batman and Superman films helped form the modern-day superhero blockbuster, and for many viewers, are the definitive live-action incarnations of their respective comic book heroes. Unsurprisingly, there are numerous instances of fan-made art, theories, and videos that pair the Reeve and Keaton incarnations of Superman and Batman together. While not all are meant to be taken seriously, there is notable interest among fans in seeing the universes merged. Long before the era of the Marvel Cinematic Universe popularizing the concept of shared continuity and casual crossovers, the superhero comic genre, especially the universes of DC and Marvel, were defined by their respective shared universes.

Related: How The Flash Can Pay Off A Canceled Batman Returns Idea

The third issue of Superman ’78 included two Easter eggs that are rather easy to miss but may have significant ramifications. The first is a copy of the Gotham Gazette magazine, seen in the background of one panel. The cover depicts what might be Bruce Wayne with the caption “The Prodigal Son Returns.” In the next panel, the cover page of a Daily Planet newspaper is shown, and while Superman’s surrender to Brainiac is the main story, below is a headline reading “Mysterious Bat-Man Terrorizes Gotham.” This confirms that a version of Batman exists in Richard Donner’s Superman continuity, and might be the one seen in Tim Burton’s movies.

Batman V Superman Trailer Retro Michael Keaton Christopher Reeve

The Gotham Gazette issue doesn’t specify that the “prodigal son” on the cover is Bruce Wayne, but this is likely the case. Bruce has most likely returned to Gotham after completing his intense training overseas. With the Daily Planet cover describing Batman in the very next panel, the issue creates a vague idea for how the two universes might coincide. Superman is a well-established and beloved hero in Metropolis by the time that Batman begins his career. Superman’s fourth and final film in the Donner universe came out (and likely took place) in 1987, matching quite nicely with the Burton Batman’s 1989 debut, which featured a Dark Knight who’d already begun his superhero career, terrorizing criminals for one or two years before the events of the film.

The face on the Gotham Gazette cover doesn’t closely resemble Michael Keaton’s Bruce Wayne, but that doesn’t necessarily mean that his character isn’t part of the same continuity as Reeve’s Superman. With their potential connection being popularized by fans and only a decade and a year separating their respective debuts, DC officially merging the film universes wouldn’t be too surprising. When DC revived Adam West’s Batman in Batman ’66, the later stories confirmed that the Lynda Carter Wonder Woman TV series from the 1970s and the George Reeves Superman show from the 1950s both shared continuity with Adam West’s Batman, despite no connection shown or implied in any of the shows themselves.

Connecting the Richard Donner Superman films and the Tim Burton Batman films would similarly be, at worst, a harmless bit of fan service for the most die-hard viewers and readers. At best, it could be the precursor to a crossover event between both comics. If the theory is proven true, Christopher Reeve’s Superman and Michael Keaton’s Batman may meet in the pages of DC’s comics someday.

Next: All 3 Versions Of Zod's Superman 2 Ending Explained

Key Release Dates