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A group of the multiverse's greatest heroes are brought together by Harbinger in an exclusive scene from tomorrow night's episode of Supergirl, "Crisis on Infinite Earths Part One." In the scene, the DEO of Earth-38 finds itself suddenly in the company of not only Supergirl (Melissa Benoist) and Tyler Hoechlin's Earth-38 Superman (that's a regular Sunday night for them, after all), but also Earth-1's Oliver Queen (Stephen Amell), Mia Smoak Katherine McNamara), and Batwoman (Ruby Rose). Kara manages to de-escalate a tense situation pretty quickly, and there's even a nice bit of comedy from Oliver, but it's pretty clear that things aren't good.

The scene also confirms a couple of things: that the child of Superman and Lois Lane (Elizabeth Tulloch) is officially named Jonathan (as he is in the comics)...and that Argo City is gone, with Alura (Erica Durance) dead. The latter revelation came in the most recent "Crisis on Infinite Earths" trailer, but fans had held out some hope that Kara's mother might have somehow survived.

You can check out the clip above.

"Crisis on Infinite Earths" has loomed over the Arrowverse for years. The series premiere of The Flash featured an allusion to the hero disappearing amid red skies in the year 2024. During the original comics event, red skies were a sign of doom to come to a world during the Crisis. At the end of last season, a couple of things happened: The Monitor (LaMonica Garrett), who had appeared in "Elseworlds," reappeared and revealed that Oliver Queen was destined to die in the Crisis...and the future newspaper at STAR Labs rolled back the expected date of the Crisis from 2024 to 2019.

In the comics, Crisis on Infinite Earths centered on a battle between the combined superheroes (and even some villains) of the DC multiverse and an immortal, cosmic threat known as the Anti-Monitor. Like The Monitor, the Anti-Monitor will be played by LaMonica Garrett in the Arrowverse. As the Anti-Monitor destroys realities, he replaces their positive matter energy with antimatter, growing his own power and sphere of influence. He was eventually stopped by the sacrifices of several heroes, including The Flash and Supergirl, as well as the merging of multiple universes to save reality by becoming a single, unified timeline. Fans have long wondered whether the events of "Crisis on Infinite Earths" might bring Supergirl and even Black Lightning to Earth-1, where the rest of the series take place. The crossover will also feature guest appearances by Tom Welling as Clark Kent, Erica Durance as Lois Lane, John Wesley Shipp as the Flash of Earth-90, Johnathon Schaech as Jonah Hex, Kevin Conroy as Bruce Wayne, and Ashley Scott as The Huntress.

“Crisis on Infinite Earths” kicks off on Sunday, December 8 on Supergirl, runs through a Monday episode of Batwoman and that Tuesday’s episode of The Flash. That will be the midseason cliffhanger, as the shows go on hiatus for the holidays and return on January 14 to finish out the event with the midseason premiere of Arrow and a "special episode" of DC's Legends of Tomorrow, which launches as a midseason series this year and so will not have an episode on the air before the Crisis.