Keith Urban tells ABC News Radio the seed for his smash duet “We Were Us” was planted in 2005 whenMiranda Lambert opened for him on tour.

“We used to do a song every night during my set,” Keith says. “I always loved singing with her, and I thought our voices went really well together.”

In the back of his mind, Keith says he was always looking for a duet that would fit their voices. When he heard “We Were Us,” he knew he’d found it.

“I just called her up and sent her the song, and she loved it.  Her and Blake [Shelton] actually came to the studio and hung out for a few hours… We sang it together and it was done.” (AUDIO IS ABC 1-ON-1)

“We Were Us” is the Aussie superstar’s first duet, but it may not be his last collaboration with Miranda.  Backstage at the CMA Awards, the Female Vocalist of the Year joked that Keith owes her a guest appearance on her next CD, since their hit single is on his album, Fuse.