"Superman's Secret Family":
Thanks to a newly invented super radio-telescope, Lois Lane discovers that Superman has been leading a secret double life on a small planet with his mermaid wife, Mooki, and their fish-tailed super-son, Nipper.
The Pride of Pittsdale is furious, now that she knows she's been played for a fool all these years. After she chews him out, the Man of Might discovers the truth and takes her to the small planet and his "family"--who are all robots.
As it turns out, when he created earlier models of his Superman robots, the X-3 robot was damaged beyond repair while subbing in for the real Man of Steel. Robot X-3 ended up on a small planet, when he was discovered by Mooki, a mermaid from the water world of Varda, where her people were all dying for lack of water.
Herself a scientist, Mooki left Varda in a rocket ship searching for another planet that could sustain her, but was unsuccessful and could only get as far as this small planet. Dying, as her last act Mooki repaired robot X-3. In memory of her--and recalling that his master had once loved a mermaid himself--the Superman robot created a Mooki robot as his wife and a super-robot boy for their son. The boy chose the name Nipper for himself.
X-3 was not restored to full power, so he could only make short trips away from their home planet, but on his world he tried to emulate his creator. Rather than destroying the robots or bringing X-3 back to Earth, Kal-El decides to let them live their "make-believe" life on their perfect, little world.
Note: Another planet that Lois views with the super telescope is Yorrp, which supports "many different types of highly intelligent creatures."