The story of how Justin Bieber ended up on Dan + Shay's new song "10,000 Hours" is simple, but surprising — at least as far as Dan Smyers and Shay Mooney are concerned.

The country duo tell Taste of Country Nights radio hosts Evan Paul and Amber that it took little more than the right text exchange to make it happen, but they still can't believe Bieber agreed to it. That was just the first surprise the pop star had for them, but we'll get to that.

The title "10,000 Hours" was inspired by a theory popularized by author Malcolm Gladwell that it takes 10,000 hours to become truly master something. Smyers, Mooney, Jessie Jo Dillon and Jordan Reynolds ("Tequila," "Speechless") were among the large group that spun that idea into a love song.

"I'd spend 10,000 hours and 10,000 more / If that's what it takes to learn that sweet heart of yours / And I might never get there but I'm gonna try / If it's 10,000 hours or the rest of my life / I'm gonna love you," they sing at each chorus. 

"Whether it's 10,000 hours to get to know that person and truly love them in the best way or it's just the rest of your life, that's the hook," Mooney explains. "It's just about learning your significant other."

While writing it, the pair started to think about what it'd be like if Bieber were on it. In fact, they envisioned him singing the second verse before they even reached out to ask. Both artists share a manager in Scooter Braun, so that's how they got in touch.

"He hit back right away like, '(He) loves the song. Wants to do it,'" Smyers shares, expressing more than a little disbelief. "So we connected and he wrote a couple of lines on it, put his spin on it.

"Do you miss the road that you grew up on / Did you get your middle name from your grandma," Bieber sings. "When you think about your forever now / Do you think of me / When you close your eyes tell me what are you dreaming / Everything I wanna know it all." 

"Coincidentally, the song is about love and he just got married and we were at the wedding," Smyers adds.

WATCH: Dan + Shay Tell Justin Bieber Wedding Stories

If you watched the above video, you know that Dan + Shay sang at Bieber's wedding. They'd planned to just sing "Speechless" and maybe "Tequila," but the groom insisted on joining them for a live performance of "10,000 Hours." It wasn't his and Hailey Baldwin's wedding song per se, but it's definitely a memorable moment for a wedding guest list that included several Jenners, Usher and more.

Dan + Shay's "10,000 Hours" with Justin Bieber will be released to all digital service providers on Friday. Smyers produced it and the whole thing was good enough to make their wives cry.

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