One of the guys who played a key role in "Iron Man" and "Iron Man 2" and "The Avengers" has made a shocking confession ... HE'S NEVER ACTUALLY WATCHED ANY OF THE MOVIES!

Paul Bettany -- who got paid TONS of cash to provide the voice for Tony Stark's computer J.A.R.V.I.S. -- dropped the bombshell to Digital Spy ... admitting he has absolutely no interest in the story and has never even read the full script for any of the 3 movies.

Bettany even joked that he feels like he's ripping off the movie studio -- "I walk in, I say some lines on a piece of paper for two hours, and then they give me a bag of money and I leave and I go about my day."

Not only that, he says it makes fan encounters a bit awkward, adding "I'm plagued by fanboys who love J.A.R.V.I.S. ... They come up and I've got no idea what they're talking about."