This year's Arrowverse crossover "Elseworlds' is exactly three weeks away from its starting episode and The CW has released a new promo showing Supergirl in a precarious position.

Imprisoned in a containment cell in an alternate version of The Flash's S.T.A.R. Labs, Kara Danvers is confronted by her captor: A twisted incarnation of her adopted older sister Alex.

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"You are as despicable as they come, you are dangerous, and you are clearly crazy," taunts Alex as she approaches the confined Girl of Steel.

"Alex, please, I know the world looks one way to you but we're sisters," begs Supergirl before an unconvinced Alex locks Kara away.

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Earlier comments by Arrowverse stars Stephen Amell and Grant Gustin had suggested the heroes wake up to find their realities changed. While all of the DCTV Multiverse at risk, it looks as though the former siblings of Supergirl's Earth find themselves in a very different relationship.

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 p.m. ET/PT. Then, it continues Monday, December 10, with Arrow and concludes on Tuesday, December 11, with Supergirl.