Behind the Scenes of The Flash-Supergirl Crossover (VIDEO)

Marisa Roffman
Supergirl & The Flash

The CW's The Flash and CBS' Supergirl collide in Monday's new hour, "Worlds Finest," when Barry (Grant Gustin) accidentally travels to Kara's (Melissa Benoist) universe.

"I think the shows really exist well together, and these two characters exist really well together," Gustin says in the behind-the-scenes video below.

"It just felt like we were literally living a comic book, bringing it to life," Benoist adds.

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While Barry is in National City, he and Kara form a joyous friendship—and he assists her with taking down Siobhan/Silver Banshee (Italia Ricci) and Livewire (Brit Morgan).

Check out the video for more from Benoist and Gustin, as well as Supergirl stars Mehcad Brooks and Jeremy Jordan.

Supergirl airs Mondays at 8/7c on CBS.