Supergirl has moved from CBS to the CW, and now its new network has a huge crossover planned. Its getting ready for a crossover between The Flash, Arrow, Supergirl, and DC’s Legends of Tomorrow. It’ll be the CW’s “biggest ever,” and it sounds like we’ll see it in December (via EW).

CW president Mark Pedowitz talked to the press ahead of a presentation and said, “Just imagine what our superhero crossover episode is going to look like come December.” He later confirmed that all four shows will be a part of the “annual crossover event.”

“Next season, Arrow, The Flash, Legends of Tomorrow, and now Supergirl will join forces in our annual crossover event, our biggest ever,” he said.

The Mary Sue reports that Supergirl will join The Flash, Arrow, and Legends of Tomorrow in its new shooting location, Vancouver. This move is believed to have happened because it’s cheaper to film in Vancouver than Los Angeles–though I can confirm that it’s still pretty expensive to live here. It also makes it easier to stage crossovers when each series is filmed in the same area. CW’s Superman series, Smallville, was filmed in Vancouver and various cities near it as well.

This won’t be the first time these superhero shows have crossed over. The Flash joined Supergirl in her show earlier this year, while The Flash and Arrow have crossed over into each other’s shows more than once.