The CW's Crisis on Infinite Earths crossover wrapped up an epic five-part run last night, but not before delivering one more major universe-shattering cameo. Ezra Miller, who plays The Flash in the DCEU, appeared in part four of the crossover event and crossed paths with Grant Gustin's version of the character, who plays the part on The CW's The Flash. This essentially makes the DCEU part of the larger multiverse in the Arrowverse, firmly binding them together for the first time.

In the episode, Barry Allen has disappeared. At one point during his travels, he hears a disembodied voice that sounds awfully familiar. Then, the two different Barrys meet face-to-face and the exchange is pretty delightful. They complement one another's costume and realize they have the same name, which leads to Ezra Miller's The Flash discovering for the first time that the multiverse is a thing before he vanishes. Here's the synopsis for the episode

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"Stuck in the Vanishing Point, the Paragons search for a way to escape. The futility of the situation is compounded by The Flash's (guest star Grant Gustin) disappearance. However, hope appears in the form of Oliver (Stephen Amell), who reveals that he has become something else. Meanwhile, the origin stories for The Monitor (guest star LaMonica Garrett) and Anti-Monitor are revealed."

This is, to say the very least of it, a big deal. Even though the characters from movies like Justice League and Batman v Superman: Dawn of Justice don't exist in the Arrowverse on a day-to-day basis, they are part of that larger multiverse. This is something of a gift for DC fans, as it means everything counts. Having Ezra Miller play Flash in the movies now takes nothing away from Grant Gustin, who has played the part for years on the small screen.

Crisis on Infinite Earths had no shortage of cameos and surprises. Brandon Routh suited up as Superman for the first time since Superman Returns, characters from other various DC shows popped up all over the place and even Robert Wuhl appeared as Alexander Knox from Tim Burton's Batman. But this one, in particular, felt huge. Grant Gustin took to Instagram to share an image of the two actors in costume from behind-the-scenes with the following caption.

"How about that? Ezra is one of a kind. So glad we could make this happen and keep it a secret until today. Thank you to DC Comics."

Truly, it is impressive that a cameo this big was kept secret until the reveal. As for when we'll see each respective Barry Allen again? The Flash was just renewed for season 7 on The CW, so Grant Gustin will be back for plenty more speedster action. Ezra Miller, meanwhile, will star in the long-gestating movie, The Flash, directed by Andy Muschietti, which is set to hit theaters on July 1, 2022. Check out the clip from the episode for yourself, as well as the photo from Grant Gustin's Instagram.