What is the last name of Rose's ex-boyfriend?  Answer the above question based on the context below:  In Bridger's Wells, Nevada in 1885, Art Croft and Gil Carter ride into town and enter Darby's Saloon. The atmosphere is subdued due to recent incidents of cattle-rustling. Art and Gil are suspected to be rustlers because they have rarely been seen in town. A man enters the saloon and announces that a rancher named Larry Kinkaid has been murdered. The townspeople immediately form a posse to pursue the murderers, who they believe are cattle rustlers. A judge tells the posse that it must bring the suspects back for trial, and that its formation by a deputy (the sheriff being out of town) is illegal. Art and Gil join the posse to avoid raising even more suspicion. Davies, who was initially opposed to forming the posse, also joins, along with "Major" Tetley and his son Gerald. Poncho informs the posse that three men and cattle bearing Kinkaid's brand have just entered Bridger's Pass. The posse encounters a stagecoach. When they try to stop it, the stagecoach guard assumes that it is a stickup, and shoots, wounding Art. In the coach are Rose Mapen, Gil's ex-girlfriend, and her new husband, Swanson. Later that night in Ox-Bow Canyon, the posse finds three men sleeping, with what are presumed to be stolen cattle nearby. The posse interrogates them: a young, well-spoken man, Donald Martin; a Mexican, Juan Martínez; and an old man, Alva Hardwicke (Francis Ford, brother of film director John Ford). Martin claims that he purchased the cattle from Kinkaid but received no bill of sale. No one believes Martin, and the posse decides to hang the three men at sunrise. Martin writes a letter to his wife and asks Davies, the only member of the posse that he trusts, to deliver it. Davies reads the letter, and, hoping to save Martin's life, shows it to the others. Davies believes that Martin is innocent and does not deserve to die.
Answer:
Carter