07/10/2007 at 04:35 PM EDT
Paging Dr. McDreamy! Meredith Grey may have one more thing to worry about in the upcoming season of Grey's Anatomy
: Actress Chyler Leigh is joining the show.
Leigh, 25, will be a series regular, playing Meredith's half sister, Lexie Grey – a new intern at Seattle Grace, a rep for ABC Television Studios confirms to PEOPLE.
Leigh first appeared in the last two episodes of the previous season, where her character's chemistry with Derek Shepard (Patrick Dempsey
) caused tension between him and Meredith (Ellen Pompeo).
She previously starred in the short-lived series Reunion
and That 80s Show
and has appeared on The Practice
and 7th Heaven.
She also starred in 2001's Not Another Teen Movie.
Leigh joins the cast on the heels of Isaiah Washington's dismissal
from the show on June 9, when he was informed that ABC was not picking up his option to return to the hit series.
The Grey's Anatomy
cast began filming the show's fourth season on Wednesday after a two-month hiatus.
News of Leigh's possible hiring was first reported by USA Today