On Sugarland's new album, BiggerTaylor Swift will join the duo's Jennifer Nettles and Kristian Bush on "Babe, a song that she co-wrote with Train's Pat Monahan. As it turns out, Sugarland didn't have to approach Swift for the song; rather, the country-turned-pop superstar came to them.

"She reached out; we have obviously known each other for many years. When she was just getting started, we had just had our first little EP out, called Premium Quality Tunes, and she still has a copy of it that we signed for her, whenever we played a couple shows together," Nettles shared backstage at the 2018 ACM Awards (quote via PopCulture.com). "And she was excited we were getting back together and reached out, and said, 'Hey, I have a song.'

"And that is a short list, ladies and gentleman, of people to whom she has said, 'Hey, I have a song. Wanna sing it?'" Nettles adds. "So we said yes."

"Babe" is the only song on the album that the Sugarland did not write -- and Bush says that's a big deal.

"We've never really put a song by anybody else on any of our records, so we weren't really used to sorting through that, and we didn't want to mess it up," he shares. "So we didn't tell anybody about it until we got finished. And she liked it, thank God. It is a good song."

As for the subject of the song, Nettles and Bush tell ET that they "don't know" and "didn't ask her" who or what inspired the track.

“I'm going to close my mouth and let her tell that story -- I'm going to let the song tell that story,” Nettles adds. "She’s very confessional in what she does with her songwriting. She lives her life out there through it, and you will see.”

Bigger will be Sugarland's sixth studio album, and their first since 2010's The Incredible Machine. Bush and Nettles put the duo on hiatus in 2012, and have pursued solo projects, acting (Nettles) and production work (Bush) in the years since. Although the two were apart for some time, they say they are working well together, just like old times.

"The dynamic and the flow creatively is much the same, and that was such a pleasant surprise after really almost seven years of not having written together, and five years of not having worked together on the road," Nettles admits. "So to find out that that flow was the same was pleasantly surprising. But I do think we got way more efficient over the hiatus."

More New Albums Coming in 2018