Melissa Benoist as Supergirl
“Arrow” and “Legends of Tomorrow” executive producer Marc Guggenheim revealed how Supergirl (Melissa Benoist) will end up in the Arrowverse for the upcoming four-way crossover event. The CW

Although “Supergirl” has already joined “Arrow,” “The Flash” and “Legends of Tomorrow” on The CW, the former CBS series remains isolated from the three shows in a sense that it isn’t technically a part of the Arrowverse. As revealed in Season 2 of “The Flash,” all of CW’s DC TV shows, except for “Supergirl,” are set on Earth-1, while the Melissa Benoist-led series is set in a completely different Earth.

Despite the difference in setting, Barry (Grant Gustin) found himself on “Supergirl’s” Earth last season when he used a tachyon device to increase his speed. But how will Kara make her way to the Arrowverse for this year’s four-way crossover?

Following an advanced screening of this week’s episodes of “Arrow” and “Legends of Tomorrow,” executive producer Marc Guggenheim revealed how Kara will end up in the Arrowverse for the week-long special event.

“Last year, ‘Supergirl’ established that Flash was able to make his way to what I call Earth-CBS, and it stands to reason that, with the proper breach technology, the reverse can happen,” Guggenheim said (via Entertainment Weekly). “[So] once the heroes [in the Arrowverse] realize that they’re up against aliens, they decide that they need an alien on their side. Fortunately, Barry knows a really nice one.”

Guggenheim explained that given Barry and Cisco’s (Carlos Valdes) experiences in traveling to and from Earth-1 and Earth-2 last season, it won't be long before the two realize that they can pluck Kara from her Earth.

According to the executive producer, the crossover event will begin at the end of an episode of “Supergirl,” where Barry and Cisco seek Kara out for help.

As revealed by Guggenheim last month, the heroes of all fours shows will be working together to take down the alien race Dominators in the crossover.

“This year, for our mega ‘Arrowverse’ crossover, we’re taking inspiration from a DC crossover from the late 1980s known as ‘Invasion!’ which featured … the Dominators, who’d previously, vexed the Legion of Superheroes,” he said (via Entertainment Weekly).

In the comics, the Dominators believe that the unpredictable evolutionary tendencies of metahumans on Earth is a threat to the state of the universe, so they try to come up with different ways to get rid of the Earth’s metahumans.

In an interview with Superhero Insider, Guggenheim said that the Dominators’ mission in the crossover event isn’t too different from their objective in the comics. “I will say that their goal is very closely related to what was established in the comics, and it does have to do with metahumans,” Guggenheim said. “It’s very, very faithful to the comics.”

The four-way crossover event is expected to air sometime in November.