Finally, the much-awaited crossover between CBS' "Supergirl," DC's "Legends of Tomorrow," The CW's "The Flash," and "Arrow" will happen. Each of the crossover episodes will reportedly share a common title called "Invasion!"

"'Arrow' episode 508 is called 'Invasion!' with the exclamation point," "Arrow's" showrunner Marc Guggenheim told Comic Book. "'Legends of Tomorrow' 207 is going to be 'Invasion!'. I'll leave it up to you to guess what The Flash is called."

The much-awaited three-part crossover event will highlight the Dominators storyline from its comics counterpart. There, a slew of extraterrestrial races suddenly invades Earth to put an end to the growing population of metahumans.

In a separate interview with Entertainment Weekly, Guggenheim stated that the "Supergirl," "Arrow," "Legends of Tomorrow," and "The Flash" event is a three-part crossover story that has a beginning, middle and an end.

"The story that's being told has a beginning, middle, and end: a beginning in Flash, a middle in Arrow, and an end in Legends," Guggenheim stressed. "But Supergirl is very much a part of the whole thing, so we are crossing over four shows - four shows in three parts."

On Oct. 22, Rick Gonzalez, who portrays Rene Ramirez aka Wild Dog on "Arrow," shared on Twitter a behind-the-scenes photo from the "Supergirl," "Arrow," "Legends of Tomorrow," and "The Flash" crossover.

Earlier reports noted that a vigilante will go head-to-head against the superheroes, especifically The Flash (Grant Gustin) and Supergirl (Melissa Benoist). Speculations are rife that the former will detest the superheroes and their special abilities instead of being astonished by it.

Be sure to stay tuned here for more news and updates about the highly anticipated "Supergirl," "Arrow," "Legends of Tomorrow," and "The Flash" crossover.