Grant Gustin's Flash to Guest Star on "Supergirl" in March

It's official: Grant Gustin will appear as The Flash on the March 28 episode of "Supergirl," as announced Wednesday by CBS. Details on the episode -- including the plot, how exactly Barry Allen finds himself in "Supergirl" territory and the extent of his role in the episode -- have not yet been released.

"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!," "The Flash" and "Supergirl" Executive Producers Greg Berlanti and Andrew Kreisberg said in a joint 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."

Fans have speculated about the possibility of a "Flash"/"Supergirl" crossover since before "Supergirl" even debuted on CBS this past October -- starting with a Variety cover from May that featured both Gustin and "Supergirl" star Melissa Benoist posing in costume alongside Berlanti (who, along with Kreisberg, is an executive producer on both shows). Yet it remained unclear if a crossover between the two networks ("The Flash" airs on The CW, a joint venture between CBS Corporation and Warner Bros. Entertainment) was even possible, with numerous reports in December stating that legal reasons may prevent the two DC Comics heroes from meeting on screen.

It's also not clear how, storyline-wise, a meeting is possible -- if "Supergirl" exists on the same Earth as "The Flash," "Arrow" and "DC's Legends of Tomorrow," it's conspicuous that none of those shows ever mentioned the existence of Superman. Yet with "The Flash" delving heavily into parallel Earths and alternate timelines in its second season, there seems to be plenty of potential explanations to bring the two shows together.

"Supergirl" airs 8 p.m. Mondays on CBS.

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