'Supergirl' season 3 release date, spoilers: Kara Danvers to face most dangerous villain yet in Odette Annable's Reign

A promotional image for "Supergirl" played by Melissa Benoist.Facebook/SupergirlCBS

The big villains of "Supergirl" have always been those that wanted to take over the cities and plunge the entire world into subordination. However, the upcoming season will have a new villain that will be unlike other earlier adversaries.

It was recently announced at the "Supergirl" panel at San Diego Comic-Con last July 21 that the main opponent of Supergirl/Kara Danvers (Melissa Benoist) will be Reign (Odette Annable), who was described as a "Worldkiller." This strongly hints that Supergirl may be having her hands full in season 3 trying to contain this potential threat.

Annable told audiences at the panel that Reign will be different from Supergirl's past villains and will have her own agenda in mind.

She stated, "It's a completely different thing that she's coming into. And I don't think people will expect to see what she's doing, which is very exciting."

Showrunner Jessica Queller further added that Reign is a "bio-engineered weapon" so she may be showcasing some very destructive powers when she goes up against the superhero this coming season.

In the last season, Supergirl had to say goodbye to her love interest Mon-El (Chris Wood) because of a gas that was released on Earth. It was safe for humans but deadly to Daxamites who tried to invade Earth under the leadership of their queen, Rhea (Teri Hatcher). Mon-El, being the son of Rhea, was also a Daxamite and therefore had to flee, leaving Supergirl heartbroken.

In the upcoming season, however, Wood revealed in an interview with Den of Geek that Mon-El may finally be wearing his superhero costume, which was a red getup with a blue cape in the comics. This implies that he will be coming back at some point in the season and reuniting with Supergirl.

"Obviously, if and when he comes back, where he's been, what happened to him, what he carries with him because of whatever experience he had will throw some really cool new dimensions into the show in a way that fans will be pretty excited about," the actor revealed.

"Supergirl" season 3 will premiere on Monday, Oct. 9, at 8 p.m. EDT on The CW.