Considering that both The Flash and Supergirl are overseen by Greg Berlanti and Andrew Kreisberg, a crossover between the two DC superhero shows seems very likely. The two series also share a similar light-hearted, breezy tone that unlike their other sibling series, Arrow, allows for superhero spectacle and conflict without all the melodrama.

Yet while Arrow and The Flash hold a crossover event each year, generating publicity for both programs, Supergirl has yet to be invited to the party. The biggest reason for this likely lies with the fact that both Arrow and The Flash air on The CW, while Supergirl airs on CBS, but the two networks are very close (the ‘C’ in CW stands for CBS, after all) and the shows’ separate network homes may no longer be the obstacle it once was.
Just about all involved behind the scenes on both Flash and Supergirl are open to the idea of a crossover, with the most recent comments from Berlanti and CW chief Mark Pedowitz suggesting it could come sooner than later. That is, assuming it happens at all, which is something that remains very much unconfirmed.

But CBS president Glenn Geller is also weighing in on the possibility and he isn’t ruling anything out, saying to reporters during a TCA press event in regard to a Flash/Supergirl crossover:

“I have to be really careful what I say here. Watch and wait and see what happens.”