Lothair, sometimes called Lothair II, d. 869, king of Lotharingia (855-69), second son of Emperor of the West Lothair I. He inherited the region bounded by the Rhine, Scheldt, Alps, and North Sea, which became known as Lotharingia (Lorraine). He was joined to Theutberga, the sister of one of his father's vassals, in an arranged marriage; after the death of Lothair I he repudiated her and married his mistress Waldrada, by whom he had a son. Theutberga appealed to Bishop Hincmar, a counselor to King Charles the Bald of the West Franks (later Emperor of the West Charles II). Charles, Lothair's uncle, hoped to annex Lotharingia if Lothair should die without an heir, which was likely since Theutberga was barren. Hincmar supported Theutberga and with the aid of Pope Nicholas I forced Lothair to reinstate her. When Lothair died suddenly his lands were divided between his uncles, Charles the Bald and Louis the German, by the Treaty of Mersen (870).