MAJOR SPOILERS ahead for Crisis on Infinite Earths Parts 4 & 5.

The Arrowverse and DCEU Flash actors, Grant Gustin and Ezra Miller respectively, feature in behind-the-scenes photos from the Crisis on Infinite Earths crossover event. The CW's annual DC TV crossover has officially concluded, and Crisis on Infinite Earths was arguably the network's biggest event to date. Not only did Crisis on Infinite Earths confirm many DC TV shows and movies to be part of the Arrowverse - many existing in other universes within the multiverse - but The CW managed to get a number of notable guest stars.

For instance, in the first half of Crisis on Infinite Earths that aired last month, Tom Welling reprised his Smallville role as Clark Kent, while Brandon Routh suited up as Superman after his starring role in 2006's Superman Returns. However, all of those universes were destroyed by the Anti-Monitor and only through Oliver Queen's sacrifice did the Arrowverse reboot. But the reboot made changes to the multiverse, including uniting all the Arrowverse shows onto one Earth, Earth-Prime. The ending of Crisis on Infinite Earths established a whole new multiverse. But perhaps the biggest surprise of Crisis on Infinite Earths was Ezra Miller's cameo as The Flash from the DC Extended Universe films like Justice League. Now fans can get a behind-the-scenes look at his cameo.

Related: Crisis Moves All Arrowverse Shows Onto One Earth

On Instagram, The Flash TV star Grant Gustin shared a series of three behind-the-scenes photos from the STAR Labs set of Crisis on Infinite Earths where he and Miller filmed the cameo. Gustin thanked DC Comics for bringing him and Miller together and making the cameo happen. See Gustin's post below.

Gustin and Miller meeting on screen is something DC fans have wanted to see ever since Miller was cast as The Flash in 2014. Both actors have been supportive of each other's versions of the Scarlet Speedster, and Miller even said he'd like to see their Flash heroes cross paths in the Speed Force. Incidentally, that's seemingly exactly what happened. The Arrowverse's Flash was traversing the Speed Force using memories to guide him to his friends when he ran across the DCEU's Flash. The pair shared a fun moment as they geeked out at each other, but the Arrowverse's Flash is confused about how the DCEU's Flash exists considering the multiverse had been wiped out at that point. It's a fair point of confusion and it's not clear how exactly the Arrowverse and the DCEU are connected.

For now, fans will have to leave that to speculation until the Arrowverse creative team or someone involved with the upcoming Flash movie offers a concrete answer. At least fans finally got the chance to see Gustin and Miller's Flash heroes unite on screen, even if it was only for a brief scene. These behind-the-scenes Crisis on Infinite Earths photos add some additional fun for fans, and give everyone a chance to really see the differences in the characters' suits. While both these Flashes are heroes of their own universes, they hail from very different DC properties. Still, it's cool to see that not only can two versions of The Flash exist on film and TV, but they can even meet on screen to give DC fans an awesome moment in Crisis on Infinite Earths.

Next: Arrowverse's New Multiverse Revealed: Which Shows Are On What Earths

Source: Grant Gustin/Instagram