 Alexandra Caroline " Lexie " Grey , M.D. is a fictional character from the medical drama television series Grey 's Anatomy , which airs on ABC in the United States . The character was created by series ' producer Shonda Rhimes and was portrayed by actress Chyler Leigh from the third through eighth seasons . She was introduced as a surgical intern in season three . Serving as Meredith Grey ( Ellen Pompeo ) ' s half sister , she transferred to the fictional Seattle Grace Hospital , after her mother 's sudden death . Eventually named a surgical resident , the character was originally contracted to appear for a multi @-@ episode story arc , but received star billing in the fourth season . 
