After about a year of speculation on if or when The CW shows like Arrow and The Flash would crossover with CBS’s Supergirl. This all began when producer Greg Berlanti along with writer Andrew Kreisberg first created The CW shows Arrow, The Flash and this years DC’s Legends of Tomorrow. However, they went on and created the show Supergirl exclusively on CBS. Today, Greg Berlanti officially announced that Grant Gustin will indeed guest star on CBS’s Supergirl as Barry Allen/The Flash:
“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.”
The question is how? As far as the timeline goes Kara Danver’s doesn’t exist within The Flash/Arrow universe is their history (Like John Constantine did on Arrow). A popular theory however is that Barry Allen may accidentally discover her “Earth”. This of course refers to the multiverse theory that is a central plot to Flash Season 2 finding heroes (like Jay Garrick) from Earth-2. This would be the most logical and simplest way to have the two heroes meet without messing up each others timelines.
The Flash will crossover with Supergirl March 28th only on CBS