Watch 1st trailer for upcoming crossover episode

The first official trailer of the crossover episode which is scheduled to air on March 28, has been released.

Episode 18 of Supergirl is titled “World’s Finest” and is officially described as follows:

“Kara gains a new ally when the lightning-fast superhero The Flash (Grant Gustin) suddenly appears from an alternate universe and helps Kara battle Siobhan, aka Silver Banshee, and Livewire in exchange for her help in finding a way to return him home.”

"Supergirl" stars Melissa Benoist as Kara Zor-El, who escapes the destruction on Krypton to join her cousin on Earth, while "The Flash" tells the story of Barry Allen, whose life changed completely when his mother died in a freak accident and his innocent father was convicted of her murder.

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also stars Mehcad Brooks, Calista Flockhart, Chyler Leigh, David Harewood, Faran Tahir, Dean Cain and Helen Slater.

"The Flash" stars Grant Gustin as Barry Allen/The Flash,Candice Patton as Iris West, Rick Cosnett as Eddie Thawne, Danielle Panabaker as Caitlin Snow, Carlos Valdes as Cisco Ramon, Jesse L. Martin as Detective Joe West, Teddy Sears as Jay Garrick, Keiynan Lonsdale as Wally West, Shantel VanSanten as Patty Spivot,Violett Beane as Jesse Quick, Demore Barnes as Tokamak, and Tony Todd as Zoom.