"Are You Sure", a Nelson original from the '60s, is one he rarely plays live. While opening for the legend last year, Musgraves asked Nelson why he never played it during his shows, which surprised him.
"He couldn't believe I knew it," Musgraves told Radio.com. "I just really loved it. It's very honest and very country, [and] it's a neat perspective. He seemingly pulled a guitar out of a cloud of smoke and started strumming. I was of course dying inside a little bit."
Before they took to the studio, Nelson had been vocal about his support for the Texas-born singer and told The Boot he was looking forward to the collaboration. "This is the one she wanted to do," he said. "It's one of those obscure songs of mine that I wrote many years ago in Nashville ... I'd love to record with her. She's a great artist."
A few weeks later, the two came together and recorded the special duet for her album. "It was meant to be a hidden track at the end," Musgraves said. "A little nugget for people who make it to the end of the record."
Musgraves recently announced dates for the Kacey Musgraves Country & Western Rhinestone Revue, which kicks off Aug. 27 in Atlanta. For ticket information and a full list of tour dates, visit her official website.