With “Supergirl” existing on a different earth than “The Flash,” “Arrow” and “Legends of Tomorrow,” it is was always a bit tricky trying to figure out exactly how all four CW superhero shows are going to crossover. Luckily, Barry Allen (Grant Gustin) knows a thing or two about traveling between worlds after visiting “Supergirl” in its first season.

That’s a trick that’s going to come in handy when the time comes to introduce Supergirl (Melissa Benoist) to the rest of the CW crew.

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“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,” executive producer Marc Guggenheim explains. “Once the heroes realize they’re up against aliens, they decide that they need an alien on their side and fortunately Barry knows a really nice one.”

While even Guggenheim admits that the way Supergirl is brought into the story shouldn’t be a “big shock” for viewers, there is one little piece of information that just might.

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While the crossover is billed as a three-part event — “The Flash,” “Arrow” and “Legends of Tomorrow” — that doesn’t mean it won’t impact that week’s episode of “Supergirl.” “The story that’s being told has a beginning, middle and end. Beginning in ‘Flash,’ middle in ‘Arrow’ and ending in ‘Legends,'” Guggeinheim explains. “But Supergirl is very much a part of the whole thing, so we are crossing over four shows in three parts.”

And it’s all going to kick off at the end of that episode of “Supergirl,” with Barry and Cisco (Carlos Valdes). That could mean Cisco is just helping Barry have the means to travel to Supergirl’s world, but who’s to say he won’t tag along for the ride?

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After all, if anyone else was going to visit Supergirl’s version of earth, wouldn’t you want it to be Cisco?

The giant crossover will kick off later in the fall.

Posted by:Chris E. Hayner

Chris E. Hayner is equal parts nerd, crazy person and coffee. He watches too much TV, knows more about pro wrestling than you do and remembers every single show from the TGIF lineup. You may have seen him as a pro-shark protester in "Sharknado 3." His eventual memoir will be called "You're Wrong, Here's Why..." TV words to live by: "I'm a firm believer that sometimes it's right to do the wrong thing."