CBS has released the first Teaser trailer for "Worlds Finest," the March 28 episode of Supergirl which will guest star Grant Gustin as The Flash.

“Worlds Finest” – 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, on SUPERGIRL, Monday, March 28 (8:00-9:00 PM) on the CBS Television Network. Grant Gustin crosses over as The Flash.

Supergirl airs Mondays at 8 pm. ET/PT on CBS.

"Worlds Finest" will air on March 28.