<Tr> <Th> Relatives </Th> <Td> Derek Shepherd (brother in - law, deceased) Zola Grey Shepherd (half - niece) Bailey Shepherd (half - nephew) Ellis Shepherd (half - niece) </Td> </Tr> <Tr> <Th> Nationality </Th> <Td> American </Td> </Tr> <P> Margaret "Maggie" Pierce, M.D. 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 . </P> <P> Pierce has been described as "perky" and "chatty", as well as focusing mostly on her academic career rather than social life, causing her to be socially inept at times and childlike . She graduated from high school and medical school early, and becomes the head of her department at the young age of 31 years old . McCreary was well received upon her introduction . </P>

Who plays meredith grey's sister on grey's anatomy