He was “smooth like butter.”

A member of K-pop supergroup BTS quietly ran in San Francisco’s famous Bay to Breakers race before performing a sold-out show at Stanford University.

Group member Suga glided through the mini-marathon on Saturday mostly unnoticed until videos of him surfaced participating in the 12K race.

One runner told ABC 7 that he had no idea he was running alongside the megastar.

“I wish I had filmed the starting line. Then I would have had a video of him at the starting line. I definitely missed out,” Mateo Coulson said.

Organizers of the Bay to Breakers race were also unaware of the pop royal in their midst.

“He was there to run, that’s our takeaway. He wanted to participate like everyone else,” Phyllis Blanchard, vice president of partnerships for Bay to Breakers, told ABC 7.

“He didn’t want to let us know ahead of time. If he did, we would have given him VIP treatment. He just wanted to fit into the crowd and run his race”

Suga, real name Min Yoon-gi, finished the race in 1:04:43, maintaining a solid 8:41-per-mile pace.

Organizers said the star’s time shows his running prowess.

“We were all excited. This is the event to attract that kind of attention,” Blanchard added. “Everyone is welcome — community members, walkers, joggers, runners — and in this case Suga. He’s quite the runner, you can tell by his finish time.”

Fans first caught wind of Suga’s appearance when BTS member RM said on a Tuesday night livestream that the band member regularly runs 10 kilometers a day and entered the race when he heard about it.

He added that Suga woke up at 6 a.m. to run the race, and then returned to Palo Alto for the group’s show that night.

The group performed in front of tens of thousands of fans for three sold-out shows at the university.