On their next encounter, the Men of Steel unintentionally teamed up when a menace from a third Earth invaded their own. Initially, Doctor Thadeus Bogus Sivana forsook his native Earth-S for the seemingly green pastures of Earth-One to challenge its native Superman, no doubt informed of that world from fellow fiend Mister Mind who had recently encounter that world's Lex Luthor briefly.
After a quick defeat and retreat, Sivana's next plan was to siphon off powers from his arch-enemy Captain Marvel, thus becoming Captain-Major-General Sivana. Once he dealt with Cap and his colleagues Mary Marvel and Captain Marvel Junior, Sivana decided to also vanquish Superman. However, instead of Kal-El he faced Kal-L, and swiftly dealt both Kals decisive blows. Only thanks to the timely intervention of Captain Marvel who saved Kal-El, and Kal-El who then saved Kal-L, were all parties retrieved from the deadly traps left them by the brilliant bald bad-guy.
It should be noted that, having witnesses Sivana's battles with both Supermen, Cap knew already off Earth-Two's Metropolis Marvel from their testy encounter on that planet during World War II when he was a minion of Hitler. Though the two heroes eventually joined forces once Cap's mind was cleared up, they never built a friendly relationship as had Earth-One's Man of Tomorrow and Earth-S Big Red Cheese. Mores the pity, for even though Kal-L and Billy Batson were products of the 1940's, it was Sivana's own Suspendium gas that preserved a youthful Marvel Family into the bronze age of heroes, when Earth-One's super-set first appeared. Hence, there was a significant age difference between the others and the elder Clark Kent.
And all three would be drawn together one final time for an epic battle that would cost one of them dearly in ways none of them could imagine....