<Tr> <Th> Significant other (s) </Th> <Td> Mark Sloan (deceased) Alex Karev Jackson Avery </Td> </Tr> <Tr> <Th> Relatives </Th> <Td> Eric Thompson (brother - in - law) Laura Grey - Thompson (niece) Derek Shepherd (half - brother - in - law, deceased) Zola Grey Shepherd (niece) Derek Bailey Shepherd (nephew) Ellis Shepherd (niece) </Td> </Tr> <P> Alexandra Caroline "Lexie" Grey, M.D. is a fictional character from ABC's medical drama television series Grey's Anatomy, portrayed by actress Chyler Leigh . Created by showrunner Shonda Rhimes, the character is introduced in season three as protagonist Meredith Grey's younger half - sister, who has transferred to Seattle Grace Hospital as a new surgical intern after her mother's sudden death . Lexie is eventually named a surgical resident in season six . Leigh was originally contracted to appear for a multi-episode story arc, but ultimately received star billing from seasons four to eight . Leigh has also reprised her role as Lexie on the spin - off show Private Practice . </P> <P> Characterized by Rhimes as a dork with issues expressing her feelings, Lexie's focal storyline in the series involved her romantic relationship with plastics attending Mark Sloan (Eric Dane). Both she and Mark sustained life - threatening injuries during an aviation accident in the eighth - season finale, which resulted in their deaths . Seattle Grace Mercy West is later renamed Grey - Sloan Memorial Hospital in their memory . The reason given for Lexie's departure after five years on the show was Leigh's desire to spend more time with her family . </P>

When does lexie grey join grey's anatomy