Hugh Jackman's final Wolverine film, which received an Oscar nomination for Best Adapted Screenplay, was simply too emotional an experience for him to consider returning.
Stewart told Digital Spy: "If we had not made Logan, then yes, I would probably be ready to get into that wheelchair one more time and be Charles Xavier. But, Logan changed all that."
He went on to recount a heartfelt moment he shared with star Hugh Jackman when they watched the film together.
"The first time that Hugh and I saw the film in public was at the Berlin Film Festival, which is where the movie premiered," he said. "Shortly after Xavier's death scene, I found myself getting very emotional but I had to keep a hold of myself because we were sitting in the middle of this cinema.
"And then I saw Hugh's hand come up to his eye and wipe away a tear. I thought, 'Dammit, the bugger's crying. Oh, let it out Patrick.' Hugh took my hand, and we held hands with the last seven or eight minutes of the film because there was so many things we were upset about."
He added: "We were moved by the story. We were moved by one another. We were moved by the movie. But we also both made the decision that we were saying goodbye to our characters as well. In that sense, it was not just the deaths of those two men in the franchise, but it was also goodbye to our part in them as well."
But while Stewart's days as Professor X are behind him, he is returning to another of his beloved sci-fi characters.