Last night, Arrowverse fans received a shock when Ezra Miller's big screen, DCEU version of Barry Allen showed up to trade a few lines of dialogue with Grant Gustin's small screen take on Flash. It was, perhaps, the greatest cameo throughout all of The CW's Crisis on Infinite Earths crossover event. And that's saying a lot since Burt Ward, Kevin Conroy, Brandon Routh, Tom Welling, and more also showed up during the various Crisis episodes.
The fun little scene even seemed to hint that Miller's character would take his official hero name after hearing the moniker of "The Flash" spoken by Gustin. But how did they pull off this epic collision of comic book realities? And more importantly, how did they keep it a secret from all of us? As it turns out, Miller wasn't added until very late in the game.
"We were series wrapped on Arrow, and we were wrapped on the whole crossover," executive producer Marc Guggenheim told Variety. "We were in post and some episodes were locked, and some were soft-locked. I got a phone call from [Warner Bros. boss] Peter Roth saying, 'I know you’re locked, but can you put Ezra into the crossover?' And I said, 'Yes.' And he said, 'How, you’re series wrapped? And you’re wrapped on the crossover.' And I said, 'Yeah, I know, but if you’re telling me Ezra Miller can be in the crossover, I can make it happen.'"
From there, it was just a matter of getting Gustin and Flash showrunner Eric Wallace up to speed.
"[Grant] was incredibly enthusiastic and on-board with it," continued Guggenheim. "And then we got on the phone with Ezra Miller and told him the scene I had written and he was completely into it. And we just went. We put together a unit of the Flash crew on the Flash set [since Arrow’s team, which had produced the rest of the hour, was gone]. And much to our surprise, no one noticed Ezra Miller was in Vancouver and no one leaked it from the crew, which we appreciate. So we were able to keep it a surprise."
A solo film for Miller's Flash (loosely based on the Flashpoint storyline by Geoff Johns and Andy Kubert) is still in the works at Warner Bros. with Andy Muschietti attached to direct, though there hasn't been much info on the project lately. As for whether DCEU Barry Allen has been totally wiped from the Arrowverse canon or not is still up for debate.
"I will leave that question to Warner Bros. and DC. They have a wonderful vision for not just Ezra’s Flash, but also the entire DC universe. Jim Lee is the man to talk to," finished Guggenheim.