Dan + Shay partied with some A-list celebrities at Justin Bieber's wedding to Hailey Baldwin, and they have stories to tell. The pop star (and the country duo's new collaborator) even surprised guests with a special performance.

Dan Smyers and Shay Mooney visited with Taste of Country to talk about "10,000 Hours," their new collaboration with Bieber, but they were more than willing to share secrets of the Sept. 30 ceremony and reception.

"It was crazy," Mooney admits. "We had, like, a formal dinner, like a sit-down, and it was gorgeous. The actual location of the wedding was beautiful. Across from me was Usher and then next to him was Kris Jenner and Kendall Jenner and Kylie Jenner ... I think they were all at our table."

The Dan + Shay lead singer reveals the ceremony was in a chapel, and that it was really fun. There was something that happened that they said they couldn't talk about, but later hesitantly revealed it might have been their performance with the groom. Yep, they sang at the Justin and Hailey wedding, much like they did for Joe Jonas six months ago. "Speechless" and "10,000 Hours" were two of the songs they performed.

"That was unplanned. Justin just came up and wanted to do it, so we ended up doing that," Mooney shares. Smyers adds that they also performed "Tequila."

"For all the single people in the crowd," he adds, laughing. "We were like 'This is not quite a wedding song, but there was a lot of tequila around the room, so it kind of works."

Watch as Mooney explains why it was very, very stressful. Be sure to subscribe to Taste of Country's YouTube channel, because Dan + Shay told us all about their song, as well.

See the Top 10 Country Songs of 2019: