Clark Kent/Superman and Lois Lane meet Barry Allen/The Flash and Oliver Queen/Green Arrow in a new sneak peek for the upcoming "Elseworlds" crossover.

The clip shows Lane threatening Flash and Green Arrow with a hammer before Kara Danvers/Supergirl intervenes. Kara introduces the two heroes to her cousin, Superman. Interestingly, Kara seems to recognize each man for his actual identity prior to their lives getting swapped, though it's unknown how at this time.

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During "Elseworlds," Oliver Queen and Barry Allen will swap lives. Thanks to Arkham Asylum doctor John Deegan, who was granted the power to rewrite reality by crossover villain The Monitor, Oliver is the Flash and Barry is the Green Arrow, and their respective teams are completely unaware of the switch. Considering that actor Tyler Hoechlin will don Superman's black suit, it seems likely that the heroes will have to fight him before the end of the crossover.

"Elseworlds" will also introduce Ruby Rose as Kate Kane/Batwoman, Cassandra Jean Amell as Nora Fries and Bob Frazer as Psycho-Pirate.

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This year's Arrowverse crossover event will involve the casts of Supergirl, Arrow and The Flash. The event will unfold over three nights, starting with a special episode of The Flash on Sunday December 9 at 8 pm ET/PT. Then, it continues Monday, December 10, with Arrow, and concludes on Tuesday, December 11, with Supergirl.