Superman: Mon-El #1

Young Clark Kent befriends a Kryptonese-speaking amnesiac whose spaceship crash-lands on Earth. Calling the survivor Mon-El, Clark decides to test whether he is Kryptonian. He takes out a lead box containing Kryptonite, but Mon-El collapses and remembers he is Lar Gand, a researcher from Daxam investigating Krypton's destruction and searching for any surviving artefacts. While following Kal-El's rocket to Earth, a sunspot caused his crash. Realizing he is dying, as lead is toxic to him, Mon-El has Clark project him into the Phantom Zone, though Clark vows to cure and release him some day.