Thatcher is admitted to the hospital with kidney stones and Lexie is shocked to discover that he is dating a 20-year-old girl. Concerned about Lexie's well-being and eager to win her back, Mark recruits his protégé Jackson Avery (Jesse Williams) to find out what is upsetting her. She reveals to Jackson that she is frustrated with the people she cares about, specifically Mark and her father, making major life-changing decisions without considering her feelings. When Lexie overhears Mark saying that he will take care of his and Callie's child regardless of what sickness it is born with, she expresses regret for neglecting to even let Mark explain the situation before she walked away from him. However, Jackson manages to convince Lexie that nobody simply has one soulmate and the two subsequently begin dating. Mark is furious and distraught when he discovers that Jackson has entered a relationship with Lexie and desperately attempts to win her back, but shortly after, Callie is involved in a severe car accident and Lexie consoles Mark. After Mark and Callie's baby is born, Mark tells Lexie that she is the only thing missing to make his life perfect. Lexie explains that she will always love Mark and will go back to him if he continues to pursue her, but she believes that they aren't suited because they have different desires. Mark then agrees to let her go, giving her and Jackson his blessing.