Dan + Shay are a country duo known for their harmonies, and during the 2016 Route 91 Harvest Festival in Las Vegas on Sunday (Oct. 2), the pair surprised the crowd with another (non-country) act known for the same thing: Boyz II Men. Together, they performed a classic from the R&B group, "I'll Make Love to You."

"Hey Vegas, don't miss our set today at @Route91Harvest. Got a surprise in the works. It will be epic," Dan Smyers and Shay Mooney teased on Twitter prior to their set. Readers can press play on the video above to watch Dan + Shay and Boyz II Men's collaboration, during which they worked the audience and handed out roses to those near the front of the stage.

"Um, we just sang with @BoyzIIMen," Smyers and Mooney tweeted on Sunday evening, along with an "OMG, that just happened!" emoji. The pair have covered "I'll Make Love to You," a No. 1, Grammy-winning hit for Boyz II Men in the mid-1990s, in past shows and during radio appearances.

Dan + Shay recently released "How Not To" as a single; the song is from their most recent album, Obsessed. They will be out on the road this fall, for their Obsessed Tour.

“We have been so humbled by the response to our new album and can’t wait to perform live for our fans this fall,” says Smyers. “Our fans inspired the title of the Obsessed album, so it was only fitting to name the tour after the album.”

More details on the Obsessed Tour are available on Dan + Shay’s website. “How Not To,” along with the rest of Obsessed, is available for purchase on iTunes now.