Lauren Alaina is the only guest vocalist on Rascal Flatts' newest studio album, Back to Us. The singer joins the Flatts' lead vocalist Gary LeVox for the heartbreaking duet "Are You Happy Now," a song that Alaina admits she was terrified to attempt.

"I was scared to death," Alaina recently told The Boot and other reporters. "When I went into the studio, right before I was going in, I called my manager, Trisha [McClanahan], and I was like, ‘I don’t even know what to say to these people when I get in here, much less how I [am] going to sing.’ I was so nervous."

Because she was on tour with Martina McBride at the time, Alaina had to leave right after her studio session. But LeVox wasn't hanging around the studio that day either, though: He had already recorded his part, which did little to ease Alaina's nerves.

"I had to hear him singing his part; it’s very intimidating. He can sing; there’s no denying that. And it’s crazy, the runs he does and stuff," Alaina explains. "I said, jokingly, ‘Thank you guys for picking me,’ and they were like, ‘Oh, well, you were like the last on the list.’ And I said, ‘Well, I’m glad I just made the list!’ And then they said they were kidding -- clearly, they were joking. But it broke the ice for me, because I hide everything with humor -- I like to crack a good joke at the wrong time -- so that was perfect for me. And then I kind of settled in, and we listened through a few times ... They were super encouraging to me."

Before they released Back to Us, Rascal Flatts shared with The Boot that they originally asked Taylor Swift to sing "Are You Happy Now" with them, for their Rewind album. When Swift declined, the country trio "put the song on the back burner" and "circled back around" to it when it was time to put together Back to Us.

"[We] cut a new track on it and sort of waited to see who we felt like would be the top of that list to go toe-to-toe with Gary," Jay DeMarcus shares, "because it’s no easy task to find a singer to get in a booth with Gary and match his vocal prowess.”

Clearly, the Flatts are pleased with Alaina's work. The group has been quick to praise her outstanding vocals when discussing their latest project, which has been a thrill for Alaina, and for her loved ones.

"I’ve seen a lot of the interviews that they’ve done, the things they said about me, and it just made it even more special," Alaina shares. "Obviously I knew that they liked my voice enough to put me on the song, but I didn’t know they felt the way they feel about me. Every day, my Nana, she’s sending me another clip that they’ve said something really awesome about me. It’s super fun, because my grandmother and my family remember me in karaoke contests when I was 12, singing [Rascal Flatts] songs and trying to keep up with Gary, so it’s really cool that I get to be on the album."

"Are You Happy Now" is available for download on iTunes.

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