<Tr> <Th> Relatives </Th> <Td> Derek Shepherd (brother - in - law, deceased) Zola Grey Shepherd (niece) Bailey Shepherd (nephew) Ellis Shepherd (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 . She graduated from high school and medical school early, and becomes the head of her department at the young age of 31 years old . </P>

When does meredith find out pierce is her sister