'Arrow', 'The Flash', 'DC's Legends of Tomorrow' and more-recently 'Supergirl' have all been entertaining audiences on The CW for quite some time now. Together they make up television's 'Arrowverse'; a universe of multiple superheroes who have all crossed over in the past and will continue to do so for as long as the series remain on air.

Grant Gustin stars as The Flash in the ArrowverseGrant Gustin stars as The Flash in the Arrowverse

The last crossover we saw was the third annual event, and brought together all four of the shows as an alien invasion threatened the peace of the planet forever. Receiving critical acclaim through the episodes as actors from each of the separate properties came together, the window of opportunity in the future was opened even further.

So what should we expect to take place when all of the shows make their comeback and another crossover event is due? Executive producer Marc Guggenheim has a little bit of information to offer.

Stephen Amell is the Green ArrowStephen Amell is the Green Arrow

"Every year we feel the pressure and I do feel like each crossover has topped the previous one," Guggenheim explained whilst chatting on EW's podcast. "Topping last year's [crossover] is a high bar, if for no other reason than what do you do that is bigger than aliens? We got some, I think, very, very exciting ideas.

"I would say, very early on in the process in actually doing last year's crossover, Greg [Berlanti] said that there's probably no way to get bigger than aliens. So the best way to make this year's crossover especially epic is, if you can't increase the bombast, increase the emotional stakes and the emotional pay-offs. A very oblique comment on where our heads are at for this season."

Exactly what that means for the storyline in regards to this year's crossover is anybody's guess, but with emotion running throughout, it's sure to be another hugely successful job done. Character development is something they do an incredible job at over on The CW, so we should expect to see some game-changing twists and turns in the four-or-so episodes that will make up the next crossover event.

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'Supergirl' returns on Monday, October 9 on The CW in the US, followed by 'The Flash' and 'Legends of Tomorrow' on Tuesday, October 10 and 'Arrow' on Thursday, October 12.