This interview contains spoilers for DC's Legends of Tomorrow Season 2, episode 7, the final installment of the "Invasion" crossover.

Now that the dust has settled from The CW's ambitious four-show crossover between Supergirl, The Flash, Arrowand Legends of Tomorrow, our heroes have not only saved the Earth from an alien attack (all in a day's work!), they've grown closer in the process -- even Barry (Grant Gustin) and Cisco (Carlos Valdes) are back to being besties.

"Their friendship has been renewed through the course of these episodes," noted Andrew Kreisberg, who serves as showrunner on The Flashand Supergirl. "So when we come back in Episode 9 [of The Flash], Team Flash is in a really good place and strong again, which they need to be, because they're going to confront Savitar in Episode 9."

SEE ALSO:3 big reveals from 'The Flash' installment of the 'Invasion' crossover

That's not the only thing Team Flash has to deal with in the Dec. 6 episode, Kreisberg told reporters during a recent press conference. "The midseason finale, Episode 9, kind of creates a new problem for our heroes that they weren't anticipating, something that they've never faced before ... that's really what's driving the episodes for the rest of the season, actually. Flashpoint won't loom as large as the challenge that presents itself in 309."

Arrowand Legendsshowrunner Marc Guggenheim teased that the Dec. 7 episode of Arrow-- which is also its midseason finale -- will show that "Oliver has a new sense of purpose" following the crossover.

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"The events of 508 basically forced him to emotionally double down on his mission," Guggenheim explained, noting that we'll also see "a reaffirmation of [Oliver's] bond with Thea, because they basically chose each other in 508. That carries through the midseason finale and, obviously, sets up things beyond it."

The rest of the heroes learned about Barry's disastrous Flashpoint decision during the "Invasion" crossover, and Guggenheim revealed that in Arrowepisode 509, "there's a fair amount of discussion about Flashpoint, given the fact that, essentially, the crossover outed Flashpoint to the Arrowcharacters who weren't Felicity. And they -- I think in some humorous ways, actually -- deal with some of the ramifications."

As for Legends, "I think the two big takeaways are obviously Stein's daughter – we haven't seen the last of her; you'll see her again in a few episodes – as well as Ray's got his suit back, and he's very, very happy to be a superhero again," Guggenheim said of the Dec. 8 episode of Legends of Tomorrow.

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After the rest of the heroes found out about Barry's ominous message from the future and the repercussions of Flashpoint, Stein (Victor Garber) and Jax (Franz Drameh) questionably decided to keep another secret -- choosing not to tell the team about the fact that Stein's daughter is a time aberration. That will be addressed in the next episode, according to Guggenheim: "The ramifications of that secret come into play."

As for Supergirl, Kreisberg admitted that the crossover "doesn't really have that big an impact because she's the one who brought the light. It was really Barry and Oliver who had to go on a journey, and she sort of brought the charm and the fun and the kickassness. So she just continues on her way."

Here's what else we learned from Guggenheim and Kreisberg after the crossover:

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We haven't seen the last of the Dominators:The alien invaders were defeated but not destroyed, leading Kreisberg to tease: "The Dominators will return on Supergirllater this season."

Don't expect a DEO on Earth-1: Kreisberg pointed out that "each of the shows has their own identity ... With Arrow, we’ve really returned to the sort of gritty crime drama that it originally was and there’s so many echoes in this season to the earlier seasons. Flashhas the metahumans. Legendshas time traveling. Supergirlhas doubled down on the alien aspect." While the door is now open for aliens to appear on Arrow, Flashor Legendsbecause of the Dominators storyline, Kreisberg said "there’s certainly no plans to have an ongoing or bring up an alien storyline on Arrow. That really feels like the purview of Supergirl."

Lynda Carter almost played a president on two Earths: If you were expecting Wonder Woman star Lynda Carter to pop up on Legends after the President was killed by the Dominators, you weren't alone -- that was the plan.

"In the original draft of the Legendsepisode, she was the vice president who became the president," Guggenheim admitted. "And the studio had what we all considered to be a very fair note, which is, it was a bit too confusing. You get into the parallel Earths of it all, but she's not the president on our Earth, she's the vice president, and in the midst of time travel and aliens it just was -- as Oliver would put it -- one sci-fi problem too much. We thought 'OK, if the studio is getting thrown by it, and confused, the audience might be too,' so we took her out. Believe me, it was not for lack of wanting to. I was planning on being on set that day."

SEE ALSO:After 100 episodes, the 'Arrow' stars look back on building a superhero universe

Earth-1 still doesn't know that aliens exist: As far as the government and media are concerned, the Dominators' ships were just weather satellites, Guggenheim said: "We had a line that we cut for time and just re-watching it, I was like, 'Oh I really wished we'd found the time another way. 'There was a line where the character, Glasses -- we call him Glasses because we're so original -- basically says, 'Cover up what? A dozen weather satellites falling out of orbit?' Because people see the ships, but no one ever really saw the Dominators. The way we're playing it going forward is that Glasses is good at his job, and when he says he's going to cover it up, he's going to cover it up."

"There's a mention of it in The Flash, that the threat of aliens brought out all the crazies, but we're sort of Doctor Who-ing it," Kreisberg agreed.

That Superman joke from Brandon Routh was just that, a joke:DC fans likely got a kick out of Ray Palmer (Routh) noting that Kara (Melissa Benoist) looks like his cousin -- a nod to the fact that Routh previously played the Man of Steel in Superman Returns.

Much like Wentworth Miller making a Prison Breakreference in an episode of Legendsinvolving a jail escape, Guggenheim said that he decided, "if we have Brandon and Melissa share the screen and we don’t make some sort of joke like that, we’re not doing our job. The truth is, that joke existed on Arroworiginally and then a certain scene got cut so then I moved it over to Legends; I just kept moving it back and forth. I’m like, 'I'm getting it in one of these episodes.'" Fan service aside, Guggenheim confirmed that the line "was a total throwaway."

Time is not on our side: While the Superman joke made the cut, there were plenty of gems that ended up on the cutting room floor for time-saving purposes, Kreisberg said.

"There was a little exchange between Sara and Kara that I really liked -- I don’t think we even filmed it -- where Sara says, 'Hey do you want to get a drink when this is all over?' and Kara says, 'I think you wanna meet my sister,'" he recalled.

"There was a funny scene between Speedy and H.R. where she says, 'So what are you doing here? What value do you bring?' He’s like, 'Well, I’m writing a book,' and she’s like, 'Oh that’ll be a big help' and walks away," he added. "It was all of those little tiny moments."

Guggenheim offered another: "There was a Supergirl moment on the Waverider that I really wanted to get in there. I’m not going to tell you what it is, because we may do it next year, but as you know Supergirl never ended up on the Waverider so we couldn’t do the moment. And obviously there were moments with Colton [Haynes] and Colin [Donnell] in Arrowthat were scripted that we obviously just couldn’t do because of Colin and Colton’s availabilities. For example, Roy was going to be Thea’s boyfriend -- that hadn’t changed -- and they met when he stole her purse, and that also hadn’t changed. I just thought that would have been fun and nice to see."

Supergirlairs Mondays at 8 p.m., The Flashairs Tuesdays at 8 p.m., Arrowairs Wednesdays at 8 p.m. and DC's Legends of Tomorrowairs Thursdays at 8 p.m. on The CW.

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