The showrunner told MTV Geek that River (Alex Kingston) will appear in the sci-fi drama's next run.
However, Moffat added that series six of Who - which revealed the character to be the daughter of Amy (Karen Gillan) and Rory (Arthur Darvill) - already covered the "big River Song story".
Discussing River's return in episode five of the new series, exec producer Caroline Skinner said: "She's so the queen of mischief in this episode."
Moffat also commented on the departure of both Amy and Rory, which will also occur in the New York-set episode five, and the later introduction of Jenna-Louise Coleman's new companion.
"When you start that story [of the companion] again, you've got a fresh take on it," he said. "You've got someone who's bemused by him, who doesn't know he has two hearts, and you meet him again through their eyes."
The writer previously claimed that the departure of Gillan and Darvill does "not necessarily" rule out further adventures with the River Song character.
Doctor Who will return to BBC One this August.