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‘Supergirl’ Showrunners on ‘The Flash’ Crossover: 5 Things to Know

”It’s exciting to think of them on screen together,“ Greg Berlanti says of early plans to feature Grant Gustin and Melissa Benoist teaming up

The “Supergirl”-“The Flash” crossover episode that many fans dreamed of is about to become a reality, and it’s been a long time coming.

“We always wanted to do it,” executive producer Greg Berlanti told reporters following a screening of the episode. “From the time we cast Melissa [Benoist, who plays Supergirl], the notion of her on screen with Grant [Gustin, who plays The Flash], you can really see them… It’s exciting to think of them on screen together.”

A crossover between CBS’ “Supergirl” and The CW’s “The Flash” or “Arrow” had long been a dream of fans of the DC Universe shows, and rumors of such an event had persisted almost since the beginning of the “Supergirl” series, which premiered in the fall.

The crossover was finally made official in February. In the episode, titled “Worlds Finest,” Gustin’s Flash shows up from a parallel universe, just in time to help Benoist’s Supergirl battle two tough foes, Silver Banshee (Italia Ricci) and Livewire (Britt Morgan), who have joined forces.

Below, Berlanti and fellow executive producer Andrew Kreisberg discussed the logistics of making the crossover happen and how the episode opens doors to future possibilities.

Putting it together was a balancing act.
“A few things definitely had to go right,” Berlanti said. “We were introducing the notion of Earth 2 and the multiverse on ‘Flash’ and that had to kind of work. We said very openly ‘Flash’ and ‘Arrow’ existed in a world where there was no Superman, or you would have heard about him. Then it was two separate networks, so that was more challenging, because that was not so convenient. You wanted the show to work, stand on its own on CBS. We thought we might wait until the second season but after Christmas we came back, we were planning out the back half of the year and we saw a way we thought we could do it, and it felt like the right time for him to enter her world. It all came together.”

Ideally, Stephen Amell‘s Arrow would have crossed over, too
“In a perfect world, it probably would have been both of them,” Berlanti said, referring to Gustin’s Flash and Amell’s Arrow. “Just because it’s not just the Flash, it’s Arrow too, but logistically that would have been a nightmare at this point, just to try to do all three shows. We had to facilitate one.”

Bonus: Logistics also cost producers the inclusion of a third villain who was originally meant to join Livewire and Silver Banshee on their rampage, but Bizarro had to be cut due to budget.

The crossover was always meant to take place on “Supergirl,” not the CW-verse
While rumors swirled about a crossover, it wasn’t made clear until the official announcement that the episode itself would be a “Supergirl” one, as opposed to “The Flash” or “Arrow.” And it was always meant to be that way.

“We never really considered it the other way, I don’t think we ever even talked about that,” Berlanti said. “Probably part of it is, it’s a little bit more fun to bring the veteran from that show to the chemistry of a new show. When we introduced Barry Allen on ‘Arrow,’ we learned something new about ‘Arrow’…. The first year of a new show is a steep learning curve, every episode you’re learning from. It was also an opportunity to learn more about the newer show.”

Bonus: When producers brought on Brandon Routh‘s Ray Palmer to “Arrow” in Season 3, part of the reasoning was to bring some of the lightness that Gustin’s Barry did in his first stint on the show.

Don’t expect immediate crossover mythology
Just because metahumans have now been introduced to “Supergirl” and aliens have been introduced to “The Flash” as a result of this crossover, fans shouldn’t expect to see these new revelations play out on their respective shows right away.

However, the logistics of how Barry ended up in National City (and in a parallel universe) in the first place will play out immediately on “The Flash,” because scheduling conflicts dictated that the corresponding episode to the “Supergirl” crossover air on Tuesday, a night after.

“They’ll see the shoutout in the episode,” Berlanti said. “It deals with Barry increasing his speed and I’m very excited about next week’s episode of ‘The Flash’ too… Had it been all in one network, we would have been able to coordinate that. I’m actually surprised that we were able to do it as closely as we were. You have to imagine that they’re parallel worlds, in different universes, and the timeline is slightly different. One is one day ahead!”

But do expect smaller crossovers going forward
While this particular crossover episode keeps Barry’s options limited in terms of discovering doppelgangers and doubles who could help him get back to his Earth, now that the door has been opened, smaller crossovers could begin to take place on the two network’s shows.

“We just talked about that recently, there is room [for smaller crossovers], absolutely,” Berlanti said.

And doppelgangers will continue to play a huge role on “The Flash,” of course.

“We have a really exciting, fun doppelganger coming up in the penultimate episode,” Kreisberg teased.

“Supergirl” airs Mondays at 8 p.m. ET on CBS.