Since it was announced that Greg Berlanti and Andrew Kreisberg would be producing a Supergirl series for CBS, it was simply a matter of time before a crossover episode with The Flash would be announced. However, many were skeptical that CBS and CW would allow their characters to cameo on competing networks.
Well, it appears that a deal has been struck as CW and CBS have confirmed the crossover is actually happening this season. Executive producers Greg Berlanti and Andrew Kreisberg released this official press statement.
We are so incredibly excited to announce something that we have dreamed of happening since we starting making Supergirl – The Flash and Supergirl are teaming up!. 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.
While anything can happen in the future, this is tentatively planned as a one-time occurrence. According to a report from Deadline, we shouldn't expect to see Kara show up in Central City, like we are accustomed to seeing in Arrow and The Flash crossovers. Deadline explains.
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 (Meliisssa 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.
This actually makes a lot of sense. The budget for Supergirl is much higher, as CBS is a much more established network than CW and pulling off Supergirl's elaborate effects, would drain The Flash's budget. However, the narrative reason is equally as compelling. Since the season two premiere, The Flash has made a concerted effort to establish that there are parrellel dimensions, where superheroes are protecting their own versions of Earth. The Flash has the unique ability to hop between these dimensions, which is presumably the explanation that they will use for his appearance in National City.
The best part about the announcement is that we will not have to wait very long to watch it. In conjunction with the release they let the public know exactly when they should tune in. The crossover event will air March 28th, only a few days after the cinematic release of [Batman v Superman: Dawn of Justice](tag:711870). Clearly DC is planning a week-long takeover, so brace yourself for all of the superheroic mashups.
The crossover episode of Supergirl will air Monday, March 28 at 9/8c on CBS.
Source: Point of Geeks