Kate Burton Kate Burton

The mystery behind Meredith's half-sister will soon be revealed!

Kate Burton has signed on to reprise her role as Ellis Grey via flashbacks for the upcoming season premiere of Grey's Anatomy, TVGuide.com has learned.

In the Season 10 finale, the new head of cardio Margaret Pierce (Kelly McCreary) was revealed to be the half-sister of Meredith (Ellen Pompeo), whom their now deceased mother Ellis Grey gave up for adoption unbeknownst to her father, Dr. Webber (James Pickens Jr).

Grey's Anatomy's Shonda Rhimes teases half-sister twist, possible new romance

"It's going to be interesting to see how it plays out," executive producer Shonda Rhimes recently told TVGuide.com of finally introducing Meredith's half-sister. "'Because we've all known about it for so long, it's always been layered in. It's not a thing where we're going in and backdating. It's literally always been layered into the story line. We can literally go back and pull out moments of the show and I'm excited to do so, and point out where it was talked about. It's not going to be so hard to do."

Burton's portrayal of Ellis Grey earned her two Emmy nominations for Outstanding Guest Actress in a Drama, the same category she's currently nominated in for playing Vice President Sally Langston on another Rhimes' series, Scandal.

Grey's Anatomy returns Thursday, Sept. 25 at 8/7c on ABC.