"Supergirl" has added a sister and a potential villain for its title character.

"Grey's Anatomy" alum Chyler Leigh and David Harewood from "Homeland" have joined the cast of the CBS superhero drama, according to The Hollywood Reporter. The show also added "Arrow" and "The Flash's" Andrew Kreisberg as a writer and executive producer.

Melissa Benoist will star as Kara Zor-El, a.k.a. Supergirl, who escapes to Earth as a young child when her home planet, Krypton, is destroyed. The Danvers family takes her in as a foster child, and they caution Kara about using her extraordinary powers (similar to her cousin Superman).

Leigh will play the Danvers' daughter, Alexandra or Alex, whose fascination with her foster sister's powers leads hMer to develop a "lifelong obsession" with science and inspires her to become a doctor.

Harewood takes on the role as Hank Henshaw, who is the Cyborg Superman in the DC Comics. On the CBS series, Henshaw is a former CIA agent who now runs the Department of Extra-Normal Operations (DEO), which tracks extraterrestrial threats on Earth.

The new co-stars join Mehcad Brooks, who will play Jimmy Olson, and Calista Flockhart as the DC Comics character Cat Grant. Laura Benanti will recur as Kara's birth mother Alura Zor-El.

CBS gave "Supergirl" a series commitment last September, and it's likely to get picked up for the 2015-2016 fall TV season. Greg Berlanti and Ali Adler will serve as executive producers.