UPDATE 2/26/2015 3:15 PM PT: In further "Supergirl" news, The Hollywood Reporter has word that Andrew Kreisberg -- who works with Greg Berlanti on "The Flash" and "Arrow" -- has joined the series as a writer and executive producer.
Additionally, KSiteTV reports that Glen Winter (a veteran of DC Comics-based TV series "The Flash," "Arrow" and "Smallville") is set to direct the "Supergirl" pilot.
Deadline has the latest two additions to the cast of CBS' in-development "Supergirl" series: Chyler Leigh, as title character Kara Zor-El's foster sister Alexandra "Alex" Danvers; and David Harewood as Hank Henshaw.
Henshaw is best known to comics fans as the villainous Cyborg Superman -- a major part of the 1992-1993 storyline "The Death and Return of Superman," one of the most famous arcs in comic book history -- but he's slated to appear on the TV series (at least from the start) in the less conspicuous role of the head of the Department of Extranormal Operations. The DEO is also adapted from DC Comics lore, as a prominent organization created by Dan Curtis Johnson and J. H. Williams III and used in their late '90s series "Chase."
A character created for the TV series, here's Deadline's description of Alex Danvers: "Fascinated by Kara's powers from a young age, Alex developed a lifelong obsession with science which inspired her to become a doctor."
Harewood has prior experience as a leader of a government organization: He played Counterterrorism Center director David Estes on "Homeland." Leigh is likely best known as Dr. Lexie Grey, a role she played for five years on "Grey's Anatomy." Leigh and Harewood join a cast headlined by Melissa Benoist, set to star in the title role, plus Calista Flockhart, set to play Cat Grant; and Mehcad Brooks, the show's Jimmy Olsen.
Developed by Greg Berlanti (executive producer of "The Flash" and "Arrow") and Ali Adler (co-creator of "The New Normal"), "Supergirl" was given a series commitment from CBS back in September.