The crowd at Glastonbury wasn't ready for that yet, but their kids are gonna love it.

Michael J. Fox, 63, joined Coldplay onstage to play guitar during the band's Glastonbury festival performance on Saturday.

Chris Martin took a moment to thank the "Back to the Future" star, who has Parkinson's disease and performed in a wheelchair.

"The main reason why we're in a band is because of watching 'Back to the Future,' so thank you to our hero forever, and one of the most amazing people on Earth, Mr. Michael J. Fox," Martin, 47, told the crowd. "Thank you so much, Michael."

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Fox's character in "Back to the Future," Marty McFly, famously plays guitar during a key scene at a school dance in 1955. Marty performs "Johnny B. Goode" years before the song's debut, inspiring Chuck Berry to record it, and stuns the crowd into silence with his forward-looking guitar solo.

"I guess you guys aren't ready for that yet," McFly tells the flabbergasted audience, "but your kids are gonna love it."

On "The Kelly Clarkson Show" in 2022, Martin said this scene "made me want to be in a band."

As Fox played the guitar at Glastonbury, Martin nodded to the movie's "Johnny B. Goode" scene by singing, "Go, Johnny, go, go, go!"

This isn't the first time Fox has performed with Coldplay. In 2016, he joined the band at a show in New Jersey to play "Earth Angel" and "Johnny B. Goode," both songs from the "Back to the Future" school dance scene. Onstage, Martin described "Back to the Future" as his and his son Moses' "favorite movie of all time."

'You had to be talented':Michael J. Fox says actors in the '80s were 'tougher'

In last year's raw documentary "Still: A Michael J. Fox Movie," Fox explored his career and battle with Parkinson's, which he was diagnosed with at age 29. He released a memoir, "No Time Like the Future: An Optimist Considers Mortality," in 2020.

In February, Fox received a standing ovation at the British Academy Film Awards as he got up from his wheelchair and presented the best film award. Host David Tennant described the actor as a "true legend of cinema."

'Still' documentary:Michael J. Fox says sobriety after Parkinson’s diagnosis was 'a knife fight in a closet'

Tom Cruise spotted at Glastonbury with Simon Pegg after Taylor Swift Eras Tour show

Other highlights from Glastonbury on Saturday include a Tom Cruise sighting.

The actor was spotted with his "Mission: Impossible" co-star Simon Pegg, who sang along to Oasis' "Don't Look Back in Anger," according to videos shared on social media.

The appearance came a week after Cruise attended Taylor Swift's Eras Tour in London alongside other stars including Mila Kunis, Ashton Kutcher, Liam Hemsworth, Hugh Grant and Greta Gerwig.

Contributing: Bryan West