Margaret Pierce, M.D., F.A.C.S. is a fictional character from the American television medical drama Grey's Anatomy, which airs on the American Broadcasting Company (ABC) in the United States. The character was created by series producer Shonda Rhimes and is portrayed by actress Kelly McCreary from the tenth season's penultimate episode onwards. It is revealed in the season ten finale, Maggie's biological parents are Richard Webber (James Pickens Jr.) and Ellis Grey (Kate Burton), making her Meredith's half-sister. McCreary was upgraded to a series regular in the eleventh episode of the eleventh season.