Princess Diana was a fan of Back to the Future — or, at least, she "wasn't booing" it, Michael J. Fox says.

In a new interview, Fox addressed the rumour that he sat next to the Princess of Wales at the 1985 world premiere of Back to the Future. The "Marty McFly" actor confirmed the story to Jimmy Fallon, sharing how the night went down.

Back to the Future: The Michael J. Fox and Princess Diana story

Fox joined Fallon on Wednesday's episode of The Tonight Show to promote his new memoir. For the interview, the host questioned Fox on rumours from his legendary career, jumping right into the Princess Diana story.

"You once watched Back to the Future while sitting next to Princess Diana. Is that true?" Fallon asked. "It's true, world premiere in London," Fox began. "She was sitting next to me, and the lights go down and the movie starts. I realize I'm one fake yawn and arm-stretch away from being on a date with her," he joked.

"But then what happened was the movie started and I had to go pee. So for the rest of the movie, I am sitting there like dying. I can't say anything to her, and I can't turn my back on her. So it was just agony. It could've been the greatest night of my life, but it was just a nightmare, a pee-floating nightmare."

As for Diana's reaction to the movie, Fox explained: "She seemed to laugh a couple times. She wasn't booing it."

Michael J. Fox's new memoir, No Time Like the Future

In the Tonight Show interview, Fox recalled that Prince Charles also attended the Back to the Future premiere, but he explained jokingly that Diana took his neighbouring seat because, "I don't think Charles wants to sit next to me for the movie."

Princess Diana and Prince Charles at Back to the Future premiere, 1985.

The 59-year-old had joined Fallon to promote his memoir, No Time Like The Future, which hit shelves on Tuesday this week. So far, the book has made headlines for Fox's comments on his future, with the star revealing he's entering a "second retirement" from acting as his health is declining

"There is a time for everything, and my time of putting in a twelve-hour workday, and memorizing seven pages of dialogue, is best behind me," Fox wrote. "At least for now ... I enter a second retirement. That could change, because everything changes. But if this is the end of my acting career, so be it."

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