Ah, the Fermat Theorem. A staple of mathematics, a cornerstone of number theory. Or is it? Meet the counterexample that shook the foundations of mathematics: The Counterexample of the Century.
It turns out, the whole thing was just a clever ruse. A trick of the great French mathematician Pierre de Fermat. He claimed to have proved a major result, but it was all a clever counterexample. Read about the scandal here.