Although they kept telling us it wouldn't happen, somehow, the planets aligned, and fans of CBS' Supergirl and The CW's The Flash will soon get a crossover episode.

That episode airs later this month on CBS and features Supergirl star Melissa Benoist and The Flash star Grant Gustin coming together for the first time. Not only that, but the shows are also crossing networks, something that rarely happens on television.

Now, a new teaser promoting that episode is available, although it doesn't really show much more than the two superheroes doing what they do best: using their respective superpowers in their efforts to save their friends and the world.

The episode, titled "World's Finest," sees Kara gaining a new ally in Barry, after he appears in National City from an alternate universe. Together, the two must battle Silver Banshee and Livewire, while also finding a way to get Barry back home.

Back before Supergirl's premiere, Greg Berlanti, who serves as showrunner for both shows, spoke about how the Flash and Supergirl needed to come together for a crossover episode to happen.

"So much has to go right," said Berlanti to Collider. "We have to make a great show. Again, I think of myself, if I were watching it, I would want to see that, but we have to get so many things right to make a good show, and so much of it is luck unfortunately."

Gustin was always open to the idea.

"Supergirl, yeah," said Gustin to IGN in January. "It also is exhausting to think about. But, if they're like, 'Hey we're doing Supergirl now and we want the Flash to be on a Supergirl episode,' I'm going to get excited about that and then after that worry about how we're going to make it work. But yeah, of course! I'm down. I'm down for any type of cool crossover as long as we can make it work."

It seems that luck was on both shows' side to make the crossover happen, but that doesn't mean that Supergirl will cross over with other DC properties on The CW, such as DC's Legends of Tomorrow and Arrow. It's clear that, by Supergirl having Barry coming from an alternate universe, Kara exists in a version of Earth that's all her own.

The Supergirl and The Flash crossover episode airs on March 28 on CBS.