Country and pop songwriter and producer Busbee -- real name Michael James Ryan -- died on Sunday (Sept. 27) at the age of 43.
The cause of death has not been made public. Earlier this year, Busbee was diagnosed with glioblastoma, an aggressive form of brain cancer.
Among Busbee's many accomplishments, the California native co-produced all but one track off Maren Morris' 2016 breakout album Hero. He also co-wrote two of the album's most important cuts: "My Church" and "80's Mercedes."
"This just doesn't seem fair," wrote Morris in a tweet after the news broke. "I will always love you and the songs and albums I was lucky to make with you, Busbee. Rest well, my sweet friend."
Keith Urban's Grammy-nominated 2016 album Ripcord was the final project co-produced by Busbee. In addition, Busbee co-wrote three songs on the album, including Urban's Carrie Underwood collaboration "The Fighter."
Beyond his work with Morris and Urban, Busbee co-wrote songs recorded by a who's-who of country music artists, including Jason Aldean ("Days Like These," "This Nothing Town"), Lauren Alaina ("Days Like These"), Garth Brooks ("People Loving People"), Florida Georgia Line ("H.O.L.Y."), Lady Antebellum ("Our Kind of Love," "You Look Good"), Rascal Flatts ("Summer Nights"), Blake Shelton ("Every Goodbye") and Carly Pearce ("Every Little Thing").
Aside from his work with Nashville's biggest stars, Busbee also co-wrote pop material recorded by the likes of 5 Seconds of Summer, Christina Aguilera, Toni Braxton, the Backstreet Boys, Shakira, Gwen Stefani, Kelly Clarkson and Pink.
Busbee's label home Warner Records also took to social media to mourn his loss.
"Today we lost Busbee, a dear friend, business partner with his company Altadena, and one of the best and brightest creative minds in music," read a statement on the Los Angeles-based label's Twitter account. "Busbee's kindness and legacy will never be forgotten and our hearts and prayers go out to his family at this very difficult time."