The Worlds Greatest Super Friends (1979)

After Superman stops a radioactive meteorite from crashing into a prehistoric planet, the blast sends Superman to the medievil planet of Camelon with no memory due to the radioactive particles in the meteor. A group of invaders led by Logan find Superman and cause him to think that he's the Black Knight and plan to use him to overthrow Arthur 7 (the planet's version of King Arthur) and take over Camelon. The other Superfriends arrive to help Arthur 7, only to be captured. After escape, it's a joust with Batman that returns Superman's memory, and all's well that ends well on Camelon.