In the last episode of the first season of Star Trek: The Original Series, Operation: Annihilate, viewers catch brief glimpses of Captain Kirk’s brother, Sam, a sister-in-law, Aurlean (although her scene is a little longer than a glimpse), and a nephew named Peter. The planet of Deneva has been overtaken by creatures that have been controlling the inhabitants and causing extreme pain and madness. While Sam and Aurlean succumb to the damages inflicted upon their bodies, presumably, Peter Kirk survives. I say presumably because his survival isn’t shown onscreen. Turns out, though, that it was written into the script and even filmed. But the scene was cut, ostensibly due to time.
In the deleted scene, Peter Kirk is alive and on the bridge wearing a smaller version of Captain Kirk’s command uniform. Kirk asks his nephew if he’s sure he doesn’t want to go back to Earth to live with his grandmother. Peter responds by saying that his father thought Deneva was the best place in the whole galaxy. And it’s revealed that Sam’s partner and wife are going to take Peter in as they always wanted a son of their own. Kirk shares a warm moment with his nephew before it’s time to go.
After Peter exits the bridge, Scotty tells Captain Kirk that Peter might want to go to Starfleet Academy later on. Kirk says he hopes not because if they hadn’t been able to find a resolution to the problem of the creatures on the planet, he would have had to destroy Deneva. He doesn’t want his nephew to ever have to make that kind of choice. According to the novel Sarek by A.C. Crispin, Kirk didn’t get his wish because, in the book, Peter Kirk is a cadet at Starfleet Academy.