Last week, CBS made the announcement that superhero fans had been waiting for, confirming that The Flash star Grant Gustin will appear in a crossover episode of Supergirl. While no story details were given for this episode, it seems that production is already under way, with Grant Gustin sharing the first photos from the set, one of which features the actor alongside Supergirl star Melissa Benoist. Hopefully the actor will share even more images from the set as production continues on this episode.

The Supergirl episode will be broadcast Monday, March 28 (8:00-9:00 PM, ET/PT) on the CBS Television Network. Ever since Supergirl was picked up by CBS, fans had wondered if it was possible for this series to cross over with Greg Berlanti and Andrew Kreisberg's shows Arrow and The Flash on The CW. While they do air on different networks, both CBS and Warner Bros. Entertainment actually own The CW, with the network's name actually a combination of the first letters of its parent companies.

The crossover was teased even more during this week's episode of The Flash, when Supergirl was spotted briefly as Barry Allen and his team travelled through the speed cannon. This seemingly confirms that Supergirl is from another alternate universe, but we don't know for sure quite yet. We'll have to wait and see if Kara Zor-El makes any more surprise appearances in The Flash as we get closer and closer to this episode.

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If this episode is a success, then it could be possible for Melissa Benoist to cross over to Central City as well, or possibly even Arrow's Star City. If these crossovers continue, it's possible that other Supergirl stars, such as Melissa Benoist, Mehcad Brooks, Chyler Leigh and Jeremy Jordan,David Harewood and Calista Flockhart could join Kara on a trip to Central City. There have been numerous crossovers between The Flash, Arrow and the new series DC's Legends of Tomorrow, but that's to be expected since they're all on the same network. This cross-network event could open up a whole new realm of crossover possibilities

While we wait for more details on this highly-anticipated episode, check out Grant Gustin's photos from the set below. What do you think will happen when Barry meets Kara? Do you think we'll get more clues to Kara's "alternate universe" in upcoming episodes of The Flash? Chime in with your thoughts, and stay tuned for more updates.