The eyes of the world were upon Woody Harrelson when he very nearly ruined a Grateful Dead concert. 

The Now You See Me star, 63, revealed on Monday’s episode of The Late Show with Stephen Colbert that he caused quite a stir at one of the classic rock band’s gigs in the ‘90s by accidentally sitting on a keyboard while high on mushrooms. 

Harrelson, who is a longtime Dead Head, explained that he met the band through a mutual friend. “He took me up to this show up in Northern California and we imbibed some fungi and were like, hanging out, and then I’m like, ‘Oh, I realize…’” he said, drifting off at the end. “Anyway! We go back to talk to everybody back there and, before you know it, I’m meeting the Dead. We chat for a minute and then they’re like, ‘We gotta get out there.’”

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The actor explained that he was taking in the gig and chatting sidestage with Bruce Hornsby, who toured with the band in the early ‘90s, when he noticed the latter had chosen to sit on the back of his chair. 

“I’m like, ‘I’ll sit on the back of my chair.’ And then suddenly this wild, discordant cacophony of crazy notes just WHAM!” He said. “Well, I think to myself, ‘Kinda genius!’ But then I notice things — and, granted, things are kicking in — and I look and I see Jerry [Garcia]’s looking back at me and Phil [Lesh] and Bobby [Weir] and they’re looking back directly at me, like if it was your dream you’d be like, ‘Whoa!’ And in life, I was like ‘Whoa!’”

The next thing Harrelson saw was a gaggle of roadies screaming expletives and running toward him. “Bruce goes, ‘Woody, you’re sitting on a live MIDI!’ Which is a keyboard,’” Harrelson said, prompting host Stephen Colbert to reply, “You’re doing an ass solo?” 

That he did. “That was my first experience with them,” he teased, “I jammed with the Dead.”

Harrelson was one of multiple stars who joined forces to pay tribute to the Northern California band when they were honored at the MusiCares Person of the Year Gala earlier this month. His speech was jam-packed full of laughs as he recalled unintentionally making his keyboard debut in the band and getting high with late frontman Garcia.

The event, which was hosted by Andy Cohen, also featured performances by John Mayer, Mick Fleetwood, Sammy Hagar, Wynonna Judd, Maren Morris, Noah Kahan, and Vampire Weekend. Weir, 77, later accepted the award on behalf of his bandmates. 

Watch Harrelson discuss playing with the Grateful Dead in the clip above.