The headline says it all, but do not read on if you want to be surprised when the Fastest Man Alive sprints into National City, just know that the episode will air on March 28, 2016.
For everyone else who speculated how this was going to do down, read on. The episode is titled Worlds Finest, and as you can see even has its own mocked up cover.
The Flash (played by Grant Gustin) will assist Supergirl (Melissa Benoist) in a fight with Livewire and the Silver Banshee with Kara helping the speedster to return to his own world.
Fans of The Flash already know that there are multiple worlds each similar in some ways and different in some others that are at least in theory capable of being reached by the Arrowverse (that is Arrow, The Flash and Vixen i.e the CW staple of DC properties). Fans of those shows will have known or at least suspected that Superman and Supergirl don’t exist there (yet… dun dun dun).
Supergirl cast includes: Melissa Benoist, Calista Flockhart, Chyler Leigh, Mehcad Brooks, David Harewood and Jeremy Jordan. The story for the episode hails from Berlanti, with the teleplay penned by executive producer Andrew Kreisberg and Michael Grassi. “Worlds Finest” was directed by Nick Gomez.