This fall, The CW will attempt something never seen on television before: a four-show crossover. That's right -- "Arrow," "The Flash," "Supergirl" and "DC's Legends of Tomorrow" will all cross paths this fall. Speaking with Entertainment Weekly, executive producer Greg Berlanti teased what brings them together.

"I'm going to probably try to have one unifying threat, as opposed to different things on different ones, which is what the first year was," he revealed, adding that they're just starting the process of writing the crossover event.

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The first crossover between "Arrow" and "The Flash" saw the heroes appear on his compatriot's show for a one-off fight with a villain, while the second officially launched "Legends of Tomorrow" by introducing Vandal Savage. This year, the crossover will bring in "Supergirl," who hails from another universe altogether.

The CW's superhero lineup kicks off another season when "The Flash" returns on Tuesday, October 4 at 8 pm EST. The four-part crossover will air later this fall.