 Muirchertach married Donnchad's daughter Flann, but relations between the two men were not good.Conflict between them is recorded in 927, 929, and 938, but it was not until 941, following Flann's death the year previously, that Muirchertach and Donnchad came to blows.That year Muirchertach raided Mide, Osraige, and Munster, taking the Munster king Cellachán Caisil hostage as a demonstration of his power and Donnchad's limited authority.