<P> Near the end of Meredith's intern year, Molly mentions that Lexie is a student at Harvard Medical School . After she graduates, Lexie is accepted by and chooses Massachusetts General Hospital as her residency spot . Following her mother's sudden death of complications stemming from the hiccups, however, Lexie decides to move back to Seattle to care for her father, taking up a surgical internship at Seattle Grace Hospital instead, one year behind Meredith who is due to begin her second year of residency . On the day of her mother's funeral, Lexie waits in the car while Thatcher, accompanied by Molly, goes to tell Meredith that she isn't welcome at the event, again missing the opportunity to meet her older half - sister . Later that night, before her internship at Seattle Grace begins, Lexie meets Derek Shepherd (Patrick Dempsey) at Joe's Bar, mirroring Derek's initial meeting with Meredith . The pair flirt and Lexie forwardly offers to buy Derek a drink, but Derek says that he is there with some friends and declines . Upon arriving at the hospital's intern locker room the next day, Lexie meets George O'Malley (T.R. Knight) during the end of his first year as an intern . After Lexie introduces herself, George immediately realizes her identity as Meredith's half - sister . </P> <P> Lexie quickly befriends George and promises not to tell anyone that he is repeating his internship after failing his intern exam . Lexie's assigned supervising resident is Meredith's best friend Cristina Yang (Sandra Oh), who doesn't take the time to learn her interns' names and thus, dubs Lexie as "Three". Although Cristina is initially rude and strict with her, Lexie eventually stands up for herself and manages to earn her mentor's respect, with Yang going so far as to acknowledge Lexie as her best student . Lexie is eager to get to know Meredith but receives a hostile response when she first introduces herself, and her later attempts to bond with her half - sister are similarly rebuffed . Lexie begins sleeping with resident Alex Karev (Justin Chambers), who discovers that Thatcher has descended into alcoholism following his wife's death and often unreasonably lashes out at Lexie . When Lexie is lectured by Meredith for not looking after Thatcher, she finally retaliates and decides to stop pursuing a relationship with Meredith . After ending her casual sexual relationship with Alex, Lexie bonds with patient Nick Hanscom (Seth Green) and is present when his exposed artery blows, causing him to suffer massive blood loss . She manages to stop the bleeding but is distraught when Nick later dies anyway . Feeling sympathy, Cristina invites Lexie to join her and Meredith in drinking and dancing, causing the sisters' relationship to begin to thaw . The following morning, Meredith goes out of her way to make Lexie breakfast, which Lexie politely eats despite being allergic to eggs, resulting in her having to be treated at the hospital . Lexie and George later agree to rent a place together, but they are only able to afford a dilapidated apartment that Lexie attempts to improve by stealing decorations and furniture from the hospital . Lexie begins to develop romantic feelings for George and secretly steals his personnel files from Chief Richard Webber's (James Pickens Jr .) office, discovering that George had only failed his intern exam by one point . She encourages George to try and convince the Chief that he deserves a second chance, to which the Chief agrees . An ecstatic George then casually plants a kiss on Lexie, completely unaware of her feelings for him . </P> <P> Lexie continues to harbor romantic feelings for an oblivious George; their relationship is a reflection of George's previous infatuation with the oblivious Meredith . She prioritizes helping George study over taking part in a rare surgery offered to her by plastics attending Mark Sloan (Eric Dane), but feels betrayed when George fails to even request that she become one of his interns after he passes his exam . Finally realizing that George doesn't feel the same way about her, Lexie gives up on her feelings for him and the pair's friendship begins to fizzle out . She soon discovers that some of her fellow interns have secretly been practicing simple procedures on each other, and begins taking part in these unauthorized operations to prove that she's "hardcore". Seeking a more daring procedure, Sadie Harris (Melissa George) later suggests that they remove her appendix . Although Lexie agrees, she quickly finds herself out of her depth and is forced to seek the aid of Meredith and Cristina to save Sadie's life, after which all of the interns in the "cabal" are put on probation . Derek finds Lexie exhausted and distraught at the day's events and allows her to move into the attic at his and Meredith's house . Lexie then begins a flirtation with Mark, and is highly impressed after watching him successfully perform a cutting - edge surgery . Later that night, she shows up at Mark's hotel room and undresses herself while repeating to him, "Teach me ." The pair grow close very quickly and enter a romantic relationship, though they are forced to keep it a secret when Derek warns Mark away from Lexie due to their large age gap and the latter being Meredith's younger sister (earning Lexie the nickname "Little Grey"). When Derek's mother (Tyne Daly) visits Seattle, Mark is initially fearful that she will disapprove of his relationship with Lexie . After meeting Lexie, however, Mrs. Shepherd tells Mark that she is exactly the kind of youthful person he should be with . When Lexie and Mark are making out in an on - call room, she accidentally gives him a penile fracture and has to seek the help of Callie Torres (Sara Ramirez) and Owen Hunt (Kevin McKidd) to treat him . Sadie then publicly takes the blame for Mark's injury to spare Lexie the burden of suffering further humiliation and guilt . Lexie later wins an intern competition organized by Izzie Stevens (Katherine Hiegl) and is congratulated by Mark . Wanting to date Mark in public, Lexie convinces him to come clean to Derek about their relationship, to which Mark agrees . But during his confession, Mark does not realize that Derek has just been devastated by the loss of a patient, and they then get into a fist fight . The two men continue to feud, resulting in Lexie beginning to stress eat until they eventually reconcile . Lexie is chosen by Mark to assist him with an extremely rare facial transplant surgery only to be judged and mocked by her peers; they believe that Mark is taking advantage of her and that she is using him . Lexie then kisses Mark in front of the other interns before stating, "They think that we're ugly but I know that we're beautiful, and we can adapt to a hostile environment ." Lexie is delighted when Meredith asks her to be a bridesmaid at her and Derek's wedding, though they ultimately give the ceremony to Alex and cancer - stricken Izzie, which Lexie attends with Mark . Lexie later asks Mark to meet her newly - sober father, which Mark initially refuses as he states that fathers have never liked him . However, Mark realizes how much he wants to build a future with Lexie, so he ends up going for dinner with her and Thatcher . Soon after, Mark decides to purchase a house and invites Lexie to move in with him only for her to decline, concerned about how fast their relationship is progressing . </P> <P> Lexie feels immense guilt following George's death, having abandoned their friendship after he failed to reciprocate her romantic feelings towards him . She is consoled by Mark and, after becoming a surgical resident, agrees to move into his new apartment with him . Lexie and the other residents grow increasingly stressed in the wake of Chief Webber's announcement that there will be a merger with Mercy West Hospital, meaning that Seattle Grace will have to layoff a large portion of its staff members . Mark encourages Lexie to relax and just try her best during this period, advising her not to worry as she deserves her job . Lexie soon finds that while she is safe from the layoffs, many of her friends have been cut from the program . To take everyone's minds off the merger, Owen takes Lexie, Mark, Derek, Meredith, and Cristina to play baseball together . Thatcher is later admitted into the hospital with liver failure stemming from his former alcoholism . When Lexie discovers that she is not a suitable transplant candidate, Meredith steps in and donates part of her liver to Thatcher to spare Lexie the grief of losing her father . Following the merger, Lexie develops a rivalry with Mercy West resident April Kepner (Sarah Drew), who desperately attempts to undermine Lexie while they are both on Derek's service . Lexie retaliates by stealing April's notebook and using its personal contents to humiliate her, though Lexie later apologizes . When a patient dies from a medical negligence mistake committed by one of the many surgeons who treated her, Webber starts a witch hunt to trace back the culprit and identify the cause of death, and Lexie is among the doctors who are questioned . It is ultimately discovered that April was the one at fault, after which Lexie and the other residents muse over the absurdity of her mistake . Despite Webber's objections, Derek recruits Lexie for his "rogue surgery" on hospital technician Isaac's (Faran Tahir) "inoperable" tumor, with Lexie acting as Derek's own caregiver during the long and exhausting procedure . Lexie is supported by Mark and, to avoid having to leave the operating room, resorts to using a diaper so that she can sufficiently hydrate herself before and during the surgery . Near the year's end, Mark and Lexie receive a shock when a pregnant teenage girl named Sloan Riley (Leven Rambin) shows up claiming to be Mark's daughter, and her parentage is soon confirmed . Mark quickly agrees to let Sloan and the baby move in permanently without consulting Lexie, resulting in her ending their relationship as she feels she is still too young to be a grandmother . An upset and drunk Lexie then engages in a one - night stand with Alex but feels guilty and confesses to Mark, who becomes furious with her despite also admitting that he had a one - night stand with Addison Montgomery (Kate Walsh). Although she secretly suppresses her feelings for Mark, Lexie and Alex assume a casual relationship that Lexie flaunts to make Mark jealous . Lexie later breaks down in front of Meredith when Alex tells her that Mark has started dating Teddy Altman (Kim Raver). After Sloan gives her baby up for adoption and leaves Seattle, however, Mark approaches Lexie and confesses his love to her . A stunned Lexie hesitantly states that Alex is now her boyfriend, to which Mark replies, "I know . I'm just saying you could have a husband ." Lexie takes part in a surgery on Alison Clark (Caroline Williams) and informs her husband Gary Clark (Michael O'Neill) that it was a success, only for Alison to suffer a stroke and fall into a coma that Derek and Webber state she is unlikely to wake from . As Alison had signed a DNR form, Lexie is forced to turn off the machines keeping her alive despite Gary begging her to stop . After failing in an attempt to sue Seattle Grace Mercy West, a grief - stricken Gary Clark later returns to the hospital with a gun, seeking revenge on Derek, Webber, and Lexie . Mark shields Lexie during the shooting and the pair attempt to save a critically wounded Alex . Lexie heads out into the evacuated hospital to search for supplies and comes face - to - face with Clark . Before Clark can shoot her, however, a SWAT team member wounds him and Lexie manages to escape . Lexie and Mark proceed to save Alex's life, during which Lexie realizes that Alex is still in love with his ex-wife Izzie, as he calls for her while delirious and on the verge of death . After having a conversation with Webber, Gary Clark eventually commits suicide, having killed eleven people and wounded another seven as well as causing Meredith to suffer a miscarriage . </P>

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