... As the knights had obtained the sovereign's permission to bring their ladies along with them, the beautiful Igerne accompanied her husband, Gerlois, Duke of Tintadiel, to one of these anniversaries.  The king became deeply enamored of the Duchess, and disclosed his passion; but Igerne repelled his advances, and revealed his solicitations to her husband.  On hearing this, the Duke instantly removed from court with Igerne, and without taking leave of Uther.  The king complained to his council of this want of duty, and they decided that the Duke should be summoned to court, and, if refractory, should be treated as a rebel.  As he refused to obey the citation, the king carried war into the estates of his vassal, and besieged him in the strong castle of Tintadiel.  Merlin transformed the king into the likeness of Gerlois, and enabled him to have many stolen interviews with Igerne.  At length the Duke was killed in battle, and the king espoused Igerne... (Age of Chivalry, Bulfinch, 1884)