ZZ Top rolled out the trailer for their upcoming documentary ZZ Top: That Little Ol’ Band From Texas earlier this week. The film — which traces their 50-year saga from their earliest days gigging around Houston through their period as MTV-era superstars and Rock and Roll Hall of Fame inductees — premieres August 13th at the Cinerama Dome in Hollywood and will play all over the country in the fall.

One moment the film will hopefully touch on is their brief, but memorable appearance in Back to the Future Part III. It comes about halfway through the movie when Marty and Doc, trapped in 1885, attend a festival in the center of Hill Valley celebrating the dedication of the town’s new clock tower. ZZ Top play an acoustic version of their song “Doubleback” with a large fiddle band as much of the town dances. Check out the scene right here. (And ignore the fact the few bits of dialogue aren’t in English — this was the best version on YouTube.)

When the band first showed up on set, some members of the crew saw their beards and thought they were merely extras dressed up for the time period. But once they started jamming with the fiddle band, they had a lot of fun. “We didn’t just want a classic fiddle band,” Back to the Future Part III director Robert Zemeckis said. “We wanted to put a little spin on it, so we were able to convince ZZ Top to come down and put some period clothes on and come and play with the band.”

Michael J. Fox loved having them around. “They are great guys,” he said. “They have the beards and everything, as advertised. They showed up and did their stuff. In between takes, they’d sit and play blues on the acoustic guitars and have mini jam sessions. It was a lot of fun.”

The complete, electric version of “Doubleback” played over the final credits of Back to the Future Part III and appeared on their 1990 LP Recycler , but not on the Back to the Future Part III soundtrack. ZZ Top are touring with Cheap Trick this summer, but don’t expect to hear “Doubleback.” They haven’t touched it in concert since 1991.

Back to the Future , meanwhile, remains one of the few classic movie franchises from the 1980s that hasn’t been revived in recent years. Zemeckis and Back to the Future co-creator Bob Gale have been been adamant that a fourth movie will never happen. “As I’m sure you all know, Michael J. Fox is not in the best of shape with his Parkinson’s,” Gale said in 2018. “The idea of making another Back to the Future movie without Michael J. Fox, you know, that’s like saying ‘I’m going to cook you a steak dinner and I’m going to hold the beef.’ You can’t do that.”