ACTION COMICS 263 (April 1960)--2nd story, "Supergirl's Darkest Day" by Binder and Mooney; r. ACTION COMICS 347 [G-33] (March-April 1967):
When the Maid of Might rescues a boy at sea, he later turns up at Midvale Orphanage. Because he speaks a foreign tongue that no one understands, he's given the name Johnny Blank.
Linda Lee is entrusted with teaching Johnny how to speak English and he figures out that she has super-powers. But the orphan keeps her secret. However, Supergirl realizes that Johnny himself can see in the dark and is from another planet.
In fact, his real name is Valzorr, from the planet Korvia, where he's a prince. When his aunt and uncle, the queen and king of that world, were lost in a teleportation accident, he was accused of their murder and fled to Earth in his space cruiser, which was wrecked in a storm.
The Action Amiga repairs the space cruiser and takes Valzorr back to Korvia where she acts as his attorney, to defend him against the murder charges.
It was actually the prime minister, Zoxxo, who messed with the teleportation device so the royal couple's atoms remained scattered in outer space. The Girl of Steel is able to put in the right computer code to return the king and queen from limbo.