Source: World's Finest Comics #172 (1967)
Type: Imaginary storyWhat if Superman and Batman were brothers?
Based on: Batman's origin
The true history: Bruce Wayne sees his parents murdered and is raised by the family butler.
Turning point: What if the Kents had registered Clark with the adoption agency? Or perhaps, what if Alfred Pennyworth didn't work for the Waynes?
Story type: Updated resumé
Watcher's mood: Not playing fair
Altered history: In this imaginary tale, Pa and Ma Kent have apparently registered Clark Kent as an adoption and so they're on the books at having done an extremely good job, enough so they are offered the custody of Bruce Wayne after his wealthy parents are killed. Superboy's all, like, does that mean I lose flying through the window privileges? And the Kents are all like, you're so super, you can keep your secret identity from your new brother.
There's some initial jealousy because while Clark has to keep his grades at "good" so that people won't think he's Superboy (which I'd thought of that in school), Bruce proves to be both the top of his class AND top dog in the school yard. Superboy becomes suspicious of him when he sees Bruce take pictures of crimes being committed and makes himself a bad guy mask. The boys take turns at night going out on patrol, and Clark is shocked to find "Batboy" coming home with a sack of jewels. Just as Batboy is pretty shocked to accidentally find the Superboy robot closet!
It's all a misunderstanding of course. Batboy's just come back from putting a criminal in jail and will take the jewels back the next day. The brothers vow to work together from now on. Cut to Bruce coming of age and getting control of his trust fund. The Kents are retiring and selling the store so he asks them to live with him in Gotham Manor. Same for Clark who soon starts work at the Gotham Gazette (and Superman who joins Batman on the fight against Gotham's underworld). Tragedy strikes when Lex Luthor, looking to get revenge on the World's Finest duo sets a bomb that kills the Kents during a charity function! Batman goes crazy! I mean, FRANK MILLER CRAZY!
Bruce can't take the fact that he's lost two sets of parents to criminals and leaves Clark in charge of the Wayne Foundation while he disappears. Superman doesn't want to see his talents go to waste, so he helps him by taking him to the year 2984, where the adult Legion of Super-Heroes changes its constitution to allow a non-powered legend like him to join.
Books canceled as a result: The sidekicks probably take the biggest hit. There are no mentions of Lois, Jimmy or Robin.
These things happen: Sounds like a Smallville story to me! But no, not really. Some stories have them meeting as teens, but no more than that.