‘Supergirl’ And ‘The Flash’ Crossover In First Teaser For Superhero Event [VIDEO & PHOTOS]

The Flash blazes over the Supergirl emblem in the first sneak peek of The CW/CBS crossover featuring the DC superheroes. When he stops short in a back alley, Supergirl quickly touches down to confront this lightning-fast man speeding through her city.

"Supergirl" will welcome Grant Gustin as Barry Allen aka The Flash for the first crossover episode between the two superheroes. Kara Danvers aka Supergirl (Melissa Benoist) will gain a new ally when The Flash suddenly appears from an alternate universe and helps Kara battle Siobhan Smythe aka Silver Banshee (Italia Ricci) and Livewire (Brit Morgan) in exchange for her help in finding a way to return him home.

The superhero event, titled "Worlds Finest," will take place in one episode of "Supergirl" on Monday, March 28 on CBS. Gustin has previously crossed over as The Flash on The CW's "Arrow" and "DC's Legends of Tomorrow."

This will be Benoist's first actual encounter with another character in the DC TV universe, although she made a brief cameo of Supergirl in a February episode of "The Flash." The cousin of Superman was seen flying alongside other alternate versions of DC comic book characters during a moment of breach in the multiverse.

The 27-year-old actress described the dynamic between Barry and Kara as a give-and-take relationship. Each is learning what works best for them as they both come into their own as superheroes. The crossover also gave her the chance to work with her former "Glee" cast mate.

"Working with Grant was so awesome and I can't wait for people to see the episode because I think it's exactly what you want to see when The Flash and Supergirl come together," Benoist said. "We had a day on set where we were in this vast landscape, it was beautiful, the scenery, and we were both in our suits and we kind of looked at each other and we're like, 'Whoa!' Take this in because this is a crazy feeling and this is pretty epic."

The crossover episode will also see Siobhan make her full transformation into DC villain Silver Banshee. Kara's former rival at CatCo. until she got canned, Siobhan will get some help embracing her evil side from another Supergirl foe, Livewire.

"It's so fun because Banshee has the confidence that Siobhan has, but not nearly as much as you need to be a villain," Ricci said about her dual-personality character. "So Livewire takes her under her wing and gives her the boost, and the looks, and the confidence that she needs to really excel as Banshee."

"The Flash"-"Supergirl" crossover will air on Monday, March 28 at 8 p.m. on CBS.

Watch the sneak peek below and check out more photos from the episode in the slideshow above.