Executive producers Greg Berlanti and Andrew Kreisberg have been talking up the possibility since last summer, but today the CW and CBS have made it official: The DC Television multiverse becomes real in March when CW’s The Flash star Grant Gustin guests on an episode of CBS’ Supergirl. Set to air March 28, details about the episode will be revealed at a later date.

At least for now, the crossover will be one-way only. While it’s likely at least in part a matter of budget (Supergirl is more expensive than The Flash), we’ve been told by sources close to the two shows that the in-universe reason is that Barry Allen/The Flash (Gustin) is able to cross dimensions while, at least for now, Supergirl (Melissa Benoist) cannot. Before fans cry foul, that’s keeping with the current storyline on The Flash, which deals with the aftermath of a dimensional rift opened between “Earth One” and “Earth Two” that is connected to The Flash’s super-speed superpowers.

“We are so incredibly excited to announce something that we have dreamed of happening since we starting making Supergirl,” Berlanti and Kreisberg said in a statement. “We want to thank Grant Gustin for making the time to come visit (on top of his already immense workload) and all of the folks at CBS, The CW, Warner Bros. and DC for working this out. And finally thanks to the fans and journalists who have kept asking for this to happen. It is our pleasure and hope to create an episode worthy of everyone’s enthusiasm and support.”

Multi-dimensional weirdness has long been a staple of the DC comic book universe. The concept has been used multiple times to reboot the line of comics, most recently creating the 2011 “New 52” continuity, on which Warner Bros’ in-development DC Universe films is loosely based. Interestingly, several different characters have operated as The Flash in DC Comics, but the DC universe films have also chosen to use Barry Allen, the same character played by Gustin. Ezra Miller plays Allen in the films.

So far, Warner Bros has treated the television and film universes as entirely separate, but it’s worth noting that at PaleyFest 2015 in Los Angeles, Berlanti hinted at the possibility both could exist in a larger multiverse: related to this, the Supergirl pilot strongly suggested that the show’s version of Superman is quite similar to that played by Henry Cavill in Man Of Steel.

Supergirl stars Benoist, Mehcad Brooks, Chyler Leigh and Jeremy Jordan, with David Harewood and Calista Flockhart. It’s produced by Berlanti Productions in association with Warner Bros. Television. Berlanti, Ali Adler, Kreisberg and Sarah Schechter executive produce, based on the characters appearing in DC Comics, and created by Jerry Siegel and Joe Shuster, by special arrangement with the Jerry Siegel Family.

The Flash is produced by Bonanza Productions Inc. in association with Berlanti Productions and Warner Bros. Television. Berlanti, Kreisberg, Todd Helbing, Aaron Helbing, and Schechter executive produce.