The director told Total Film that his first cut of X-Men was "languid and terrible", but the negative feedback he received sparked the idea for Patrick Stewart's opening voiceover as Professor Xavier.
Singer said: "I didn't mean for it to be screened that early, and then someone posted a review on the internet. This horrible, mean, awful, terrible review of the slow, miserable first cut of X-Men inspired one thing.
"It was something the reviewer said, like, 'We don't even know what these mutants are!' And that gave me an idea for the preamble, Xavier's preamble - 'Mutants, they are the key to our evolution...' I thought, this'll become our thing, like the gun barrel at the start of James Bond, and we'll have it in front of every movie.
"So as much as I hate those evil internet reviews, it actually helped me come up with that!"
Singer is currently directing Jack the Giant Killer and served as a producer on Matthew Vaughn's upcoming X-Men: First Class.
Watch the X-Men: First Class trailer below: