<Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> Lexie Grey is the daughter of Thatcher Grey (Jeff Perry) and his second wife, Susan Grey (Mare Winningham). She grew up with her younger sister, Molly Grey - Thompson (Mandy Siegfried) and throughout her childhood was kept unaware that she also had an older half - sister, Meredith Grey (Ellen Pompeo), born to Thatcher and his first wife, Ellis Grey (Kate Burton). Lexie is first mentioned when Molly is admitted to Seattle Grace Hospital, with Susan informing Meredith that Lexie is a student at Harvard Medical School . At some subsequent point, Lexie learns of Meredith's existence . She graduates from medical school and is accepted to take her surgical internship at Mass General hospital, but following her mother's sudden death from complications stemming from the hiccups, Lexie instead opts to move back to Seattle to be closer to her father, taking up an internship at Seattle Grace Hospital, one year behind Meredith who is due to begin her residency . </P> <P> Lexie has an eidetic memory, which is often used as a valuable resource and earns Lexie the nickname "Lexipedia ." </P> <P> In contrast to Meredith, Lexie came from a loving home with a happy upbringing . Meredith once said of her: "She was raised right . With parents and rules and smiley face posters on her wall ." Her idealistic upbringing leaves her unprepared to deal with the many hardships she faces during the course of the show, and she often has difficulties understanding and accepting the darker side of human emotions . </P>

When did lexie and mark get back together