Keith Urban's newest single "The Fighter" was born from a conversation he had with his wife Nicole Kidman more than a decade ago. The singer says they were just beginning their relationship when she told him that when things get tough, she needs him to hold her tighter.

Carrie Underwood joins Urban on "The Fighter," the fifth single from Ripcord. You may recall Kidman teaming up with Urban for a lip-sync of the song when the album was released last May, however. It's an unexpectedly personal song.

"The song is about wanting to heal somebody, wanting to take care of somebody, wanting to protect somebody," Urban tells Billboard. "It’s really like a vow in so many ways."

The trade magazine reports that Urban put most of the song together with writer busbee in London during the fall of 2015. Kidman was starring in a production of Photograph 51 at the time. Part of the song was written during an Uber ride to the songwriting appointment, and it was later finished in Los Angeles. Underwood came on after that, although her inclusion was not without obstacles. Urban struggled to find a whole in her schedule for her to cut her parts, but eventually, thankfully, she was able to cut lines in St. Louis.

In February, the duo (Urban and Underwood) debuted the song on national television during the Grammys. It's currently a Top 20 single on the Billboard Country Airplay chart.

See Photos of Keith Urban and Nicole Kidman at the Oscars

Keith Urban's Most Unforgettable On and Off-Stage Moments