 Grey, Yang, Karev, and Stevens are all promoted to residents, in the season four premiere, while O 'Malley is forced to repeat his internship year, following his failing of the intern exam. Subsequently, Torres and O'Malley divorce one another, due to him having a sexual affair with Stevens, initially concealing it from Torres. Early in the fourth season, cardiothoracic surgeon Erica Hahn becomes Torres'love interest. During the fifth season, Hahn departs from the series, and O'Malley retakes his intern exam, passing, joining his fellow physicians as a resident. Two new characters are introduced, former United States Army trauma surgeon Dr. Owen Hunt, and pediatric surgeon Dr. Arizona Robbins. Hunt becomes a love-interest for Yang, while Robbins becomes a love-interest for Torres. When Stevens is diagnosed with stage four metastatic melanoma, she and Karev wed one another at the conclusion of the fifth season. In addition, Meredith and Shepherd marry, with their vows written on a post-it note.
