Supergirl will be taking on a world killer in Season 3.

The superhero show has cast Odette Annable (Astronaut Wives Club) as the DC Comics villain Reign for next season, has learned. Reign will be the "big bad" for Season 3 as the show adapts the Worldkiller storyline from the comic books.

"Greg and I have wanted to work with Odette for years. We are beyond excited to have her join our cast in the scary, powerful and heartbreaking role of Reign," executive producer Andrew Kreisberg said.

The final scene of Supergirl's Season 2 finale showed that another Krypton baby made it off the planet before it exploded. We can now safely assume that baby was Reign. In the comic books, "Worldkillers" are biological weapons — genetically modified aliens that become blood-thirsty and uncontrollable threats to all living things.

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Kara's (Melissa Benoist) father Zor-El had a part in creating the Worldkillers before they were banned by Kryptonian Science Council, and felt guilty for their creation but was unable to destroy them as he was ordered to do.

Reign is the leader of the surviving Worldkillers but has no recollection of how she was created or where she comes from. She tracks down Supergirl to find out their origins, but when Supergirl can't give her the answers she desires, she decides to try and take over Earth.

Supergirl returns this fall on The CW.

(Full disclosure: is owned by CBS, one of the CW's parent companies)