ABC's hit medical drama is getting a little more Grey.

Former "Reunion" star Chyler Leigh, who appeared in the final two episodes of "Grey's Anatomy" last season, is joining the show as a regular for 2007-08, ABC says. She'll be playing Lexie Grey, the younger half-sister of Meredith (Ellen Pompeo) and a new intern at Seattle Grace Hospital.

Her appearances on the show in May were brief but impactful. In the show's penultimate episode, she flirted with Derek (Patrick Dempsey) at a bar -- shades of her sister in the pilot -- and then revealed her last name to George (T.R. Knight) near the end of the finale.

"Grey's Anatomy" began production on its fourth season this week and will follow Meredith, Cristina (Sandra Oh), Alex (Justin Chambers) and Izzie (Katherine Heigl) in their first year as residents at Seattle Grace. With their new title come interns to boss around -- including George, who has to repeat his internship after bombing his exams at the end of last season.

Leigh's most recent series credit was FOX's "Reunion," which aired during the 2005-06 season. She also starred in the short-lived "Girls Club" and "That '80s Show" for FOX and did a stint on ABC's "The Practice" in 2003.

Her credits also include "Not Another Teen Movie" and appearances on "7th Heaven," "Safe Harbor" and "North Shore."