If you watched The Flash and wondered, "What the f*** was that?" when it ended, you probably aren't alone.
During the final act, the older Barry Allen concludes that, in the timeline he created by travelling back to save his mother, there's nothing he can do to stop General Zod's destruction of Earth or the deaths of Batman and Supergirl. His younger self refuses to accept that and continues to try over and over to alter the outcome of the final battle with no luck.
As a result, he eventually becomes the Dark Flash and that monstrous speedster reveals he was the one who pulled Barry into the past to make sure he'd be there to help him set things right. It's typical time-travel nonsense that makes no sense when you stop and think about it, but the younger Barry saves his older self, wiping Dark Flash out of existence and allowing the Scarlet Speedster to undo his previous actions (meaning his mother will still be mysteriously killed).
However, he makes one final tweak to the timeline by ensuring his father's face is shown on a store's security camera, thereby giving him an alibi and exonerating Henry for Nora's murder back in the present. Earlier in the film, we learned his face couldn't be seen, but Barry putting the can he was looking for higher up on the shelf means it now can.
The change is small enough not to break the timeline or create a new one...or so Barry thinks.
Leaving the courtroom, Bruce Wayne calls him and pulls up in his car, and out steps George Clooney. It turns out The Flash's actions created another new reality, albeit one where Clooney's Bruce is Batman. Barry seems baffled by the entire situation and forces a smile before his tooth, which he superglued back on earlier in the movie, falls out.
Does this mean the hero is trapped in an alternate reality? Is Clooney the new DCU's Batman? We can't definitively answer those questions just yet but original plans called for The Flash to end with Keaton's Bruce stepping out of the car. He was going to be joined by Supergirl, with both wondering how they were part of this new reality. From there, they'd have officially entered the DCEU, ending the movie with a cliffhanger.
You may even recall seeing this exchange in set photos which first surfaced in 2021.
This is a much better conclusion than Batman and Supergirl dying and never being shown again, explaining Keaton's presence in both Batgirl and Aquaman and the Lost Kingdom. As for Kara Zor-El, original plans called for her to permanently replace Superman, though Henry Cavill was to be added to this shared world again after Black Adam.
As for the post-credits scene, the now largely pointless stinger picks up with Barry attempting to tell Arthur Curry about what happened following a drunken night out. The King of Atlantis eventually collapses into a puddle, prompting the Scarlet Speedster to reveal he was his father's pet dog in the other timeline.
In an earlier cut of the movie, we'd have actually seen The Flash return to his apartment to get Aquaman more beer, only to notice a video message waiting for him from Bruce. However, rather than Keaton's Dark Knight, it was going to show Ben Affleck's version pleading with Barry to find the timeline he left behind, thereby setting the stage for a Crisis on Infinite Earths project which, under DC Studios' watch, will no longer happen.
You can read our review of The Flash by clicking here. The movie is now playing in theaters.