Supergirl Cameos In The Flash Tonight, And What That Means For Their Crossover Story

Warning: Spoilers ahead for tonight's episode of The Flash, titled "Welcome to Earth-2."

Yes, folks, that was Melissa Benoist as Supergirl that you just saw on The Flash.

And, since Barry Allen was moving through a breach in the multiverse, it's likely safe to assume that she comes from a different Earth.

While many fans assumed that Supergirl and The Flash take place on different Earths because the title of their March 28 crossover episode is "Worlds Finest," without the apostrophe, seeing her out there in the multiverse alongside an alternate Green Arrow and the John Wesley Shipp version of The Flash feels like hard confirmation.

The idea that Supergirl exists on a different earth is a mixed bag for fans. It means that the character is unlikely to team up with the grounded and gritty Arrow or the time-traveling DC's Legends of Tomorrow. Legends EP Phil Klemmer recently told reporters that the multiverse was The Flash's thing, and their time traveling will remain on Earth-1 for the foreseeable future.

Did you catch all of that? #TheFlash pic.twitter.com/v8y6AM8ezm

— The Flash (@CW_TheFlash) February 10, 2016

It also explains why the general public is so reluctant to accept The Flash and other super-powered heroes. In the world of Supergirl, her cousin has been Superman for years and is a beloved public figure. Many fans have pointed out during the run-up to finalizing a crossover that it could create continuity hiccups in the Arrowverse to have them share a world.

Of course, that isn't to say there's no Kryptonians on Earth-1. Remember, Rip Hunter on DC's Legends of Tomorrow last week told the team that he has "seen Men of Steel die and Dark Knights fall."