When Gwen Stefani tweeted a photo of the track listing for boyfriend Blake Shelton's upcoming new album on Tuesday (April 19), she didn't just reveal the record's full slate of songs, she also confirmed the rumors that the couple had written a tune together. Shelton himself has now provided some more information about their collaboration -- and what it took to make it happen.

"I'm insecure about my writing and who I write with, and I don't know -- I'm just weird about it sometimes," Shelton admits to People. "I think Gwen has a smaller circle, too, when it comes to writing, and the fact that we went there that early as we were getting to know each other, it's just remarkable."

The country star tells ET that while the two of them "reach[ing] out to each other as writers, it may never happen again, who knows," the two found it remarkably easy to write together, even with their different musical sounds.

"As different as we are musically, we're a fan of the same type of songs," he explains to People. "We have these playlists that we send each other that are stuff that we loved growing up, and they're so similar, so I think it made it easy for us to collaborate."

To ET, Shelton called his and Stefani's collaboration, titled "Go Ahead and Break My Heart," "a full-blown duet," adding that "I hesitate to brag on it too much, but I really think that it's as good of a song as I've ever written in my life."

"The song's important to us," Shelton notes to People, "and the fact that we wrote it together is so important to both of us."

As for that tweet from Stefani? It was all Shelton's idea.

"We finally got a mock-up of the album, what the artwork was going to look like. And we flip it over, and it has all the songs. I said, ‘You know what? Take a picture of that and tweet it,'" Shelton recalls to ET. "'It'll be our way to announce that yes, we have a duet together.'"

Shelton's new album, If I'm Honest, is set for release on May 20.

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