Carrie Underwood is mourning the loss of her friend Brett James, who wrote one of her biggest songs.

Grammy-winning songwriter James died in a plane crash on Thursday, according to the Nashville Songwriters Hall of Fame. He was 57.

Underwood and James collaborated on the 2005 hit “Jesus, Take the Wheel,” as well as her 2009 song “Cowboy Casanova.”

“Some things are just unfathomable. The loss of Brett James to his family, friends and our music community is too great to put into words,” Underwood wrote in a tribute shared on social media on Friday.

“Brett was the epitome of ‘cool.’ I see him in my mind riding up to my cabins to write on his motorcycle…his hair somehow perfectly coiffed despite being under a helmet for however long. I always loved hearing him sing ‘Cowboy Casanova’ because a sassy girl anthem should’ve sounded ridiculous coming from a macho dude like him, but somehow, he even made that cool,” she continued.

James worked with other top artists, including Taylor Swift, Bon Jovi and Keith Urban. He also cowrote Kenny Chesney’s “Out Last Night” and was regarded as one of the industry’s most sought-after collaborators.

“Brett’s passing is leaving a hole in all of us that I fear won’t ever go away. It will forever be a reminder that this life is but a moment…we have to make the most of each day we’re given here on earth. Each day is a gift,” Underwood concluded her post.

“Love you, man. I’ll see you again someday.”