Iron Man, Vol. 1 #150 (1981)

Knightmare
Iron Man and Dr. Doom find themselves transported back to Camelot, and are guests of King Arthur. Doom breaks free in search of Morgana Le Fay, one of the greatest sorceresses in history, so that he may learn how to free his mother's soul from eternal torment. Morgana agrees, provided Doom leads her army against Arthur in exchange. Iron Man fights alongside Arthur and his knights for a while, but then takes the fight directly to Le Fay. Their confrontation is short but sweet, as Morgana flees. Doom recognizes the futility of staying in the past any longer, so the two call a truce and combine the technology in their armours in order to return to the correct time.
Release Date: 1981