DC just pulled off its ballsiest move yet, something that even the MCU has yet to do; Introduce the concept of the multiverse from the comics and connect every live-action superhero property across film and television in the process. The biggest surprise of this event was Ezra Miller's cameo in the Crisis on Infinite Earths crossover currently unfolding across the CW's Arrowverse. Executive producer for the series Marc Guggenheim recently sat with Variety to reveal how Miller's participation in the Arrowverse was pulled off.

We were series wrapped on Arrow, and we were wrapped on the whole crossover. 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."

Clearly, the prospect of adding the movie version of Flash, and by extension, the entire DCEU to the Arrowverse was very welcome to the show's creative team. Still, despite getting the nod from Warner Bros., there was one more important person who needed to sign off on the idea. TV-Flash himself, Grant Gustin:

I called Eric Wallace who is the showrunner of The Flash, and he called up Grant Gustin - because the one thing that was our only concern was the thought we didn't want to do it unless Grant was 100 percent on-board with it. And he was. He was incredibly enthusiastic and on-board with it."

Many would argue that Gustin's interpretation of The Flash is far more popular than Miller's, and it makes sense that he would have a say in whether he would be willing to share screen space with a rival Flash.

With Gustin showing enthusiasm for the idea of TV Flash meeting his movie counterpart, the process of including Miller's cameo became simple. And now, the DCEU is officially a part of the Arrowverse, along with almost every other live-action adaptation of DC properties that have ever been created, including Tom Welling and Brandon Routh's Supermen, Micheal Keaton and Adam West's Batmen, Constantine, Lucifer and many more.

It remains to be seen whether Ezra Miller's cameo was simply a way to garner some attention for his upcoming solo Flash movie, or if the introduction of the multiverse into the DCEU is a set up for major changes to DC's movieverse, giving the company a way to introduce new versions of Superman and Batman to the continuity now that Ben Affleck and Henry Cavill have seemingly left the franchise for good.

For now, instead of pondering these questions, fans can simply enjoy watching the two Flashes geek out over each other's costumes, and Gustin giving Miller's Flash the idea for what his superhero name should be.