Alexandra Caroline Grey, M.D. is a fictional character from ABC's medical drama television series "Grey's Anatomy", portrayed by actress Chyler Leigh. Created by series producer Shonda Rhimes, the character is introduced in season 3 as the titular protagonist's younger paternal half-sister. She transfers to Seattle Grace Hospital as a new surgical intern after her mother's sudden death, and is eventually named a surgical resident in season 5. Leigh was originally contracted to appear for a multi-episode story-arc but ultimately received star-billing from seasons 4 to 8. She has also reprised her role as Lexie on the spin-off show "Private Practice".