Merle Haggard's Bakersfield doctor, Marion C. Barnard II , 65 , died Thursday.
The pair have known each other since the 1970s, according to a 2008 Californian story.
Haggard surprised Barnard for his 60th birthday that year with a concert at Fishlips, a since-closed restaurant in downtown Bakersfield.
"I walked in and all of a sudden, everybody's giving me attention and I hear this familiar voice say [singing] 'Happy birthday to you ... ," he said.
For the story Barnard remembered a different concert in Fresno at which the country music legend asked him to be his doctor.
"He said, 'You know, you and I have been friends for a while,'" Barnard said. "'I think you're a good young doctor and I'd like to have someone who cares about me besides being a good doctor.'"
A full obituary of Barnard will appear next week.