'Arrow,' 'The Flash,' 'Supergirl,' 'Legends Of Tomorrow' Crossover Teased By Stephen Amell

(Photo : Getty Images/ Dimitrios Kambouris) Stephen Amell recently took to Twitter to share a photo teasing what appears to be the first shooting day of the four-way crossover event between "Arrow," "The Flash," "Supergirl" and "Legends of Tomorrow."

Has the production on the highly anticipated four-way crossover event between "Arrow," "The Flash," "Supergirl" and "Legends of Tomorrow" already started?

Earlier today, "Arrow" lead star Stephen Amell took to Twitter to share a photo teasing what appears to be the first shooting day of the mash-up event between all the DC TV shows airing on The CW. The pic shows Amell, Grant Gustin, Melissa Benoist, Caity Lotz and Brandon Routh's feet wearing their respective superhero boots.

pic.twitter.com/7TEaZWbjNc

— Stephen Amell (@StephenAmell) August 7, 2016

Lotz also shared a photo of herself with Amell on Instagram today.

A photo posted by Caity Lotz (@caitylotz) on Aug 7, 2016 at 2:44pm PDT

Details about the upcoming crossover event are scarce, but executive producer Greg Berlanti recently revealed to Entertainment Weekly that he will attempt to come up with a single threat for the week-long mash-up event.

"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," Berlanti said.

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As for what that threat is, "Legends of Tomorrow" executive producer Marc Guggenheim said (via Comic Book Resources) at San Diego Comic-Con last month that "it's an external threat from outside the shows that will involve Supergirl [Benoist] coming over to "The Flash," then "Arrow" then "Legends of Tomorrow."

"Arrow" executive producer Wendy Mericle pointed out that the crossover event will coincide with "Arrow's" 100th episode, so fans can expect the crossover to celebrate the ever-expanding DC TV universe of The CW.

"I can tell you it's our hundredth, which is exciting," Mericle said. "We are just sort of getting into it right now. It's going to be the biggest one we've done; it's going to involve all four shows, which is unprecedented. Every year we think, 'oh, we've figured this out, we know how to do two shows, now we're adding in three shows, and we've never had to do four. It's going to be interesting. It will be a four-part story; 'Supergirl' airing first will obviously be the kickoff."

What do you want to see in the four-way crossover event? Tell us in the comments below!