"A true musician. A true friend. Happy birthday, (Reba)," wrote Parton on Instagram. The caption accompanied a throwback photo of both well-rounded entertainers.
Parton's photo of choice bears the signature of McEntire and a special message: "Dolly! You'll always be my hero! Love ya, Reba."
The friends have known each other since McEntire's Grand Ole Opry debut in 1977. Since then, Parton's made a special guest appearance on the sitcom Reba and on the podcast Living & Learning With Reba McEntire, which both featured another McEntire confidant, Melissa Peterman.
Parton, McEntire and Carrie Underwood were co-hosts of the 53rd annual CMA Awards in 2019. The trio were among the high points of the ABC broadcast's all-star medley celebrating the women of country music.
During Parton's podcast appearance, McEntire praised her fellow country star's 1969 album My Blue Ridge Mountain Boy.
"I wore it out. Your songwriting, it is just so heartfelt, and it pierced my heart on every song," McEntire said (as reported by Today). "Those songs, I can still remember the words to 'em when I can't remember the words to a song I have out as a single nowadays."
McEntire posted her own special message back in January when Parton turned 75.
"Happy birthday Dolly Parton, I love you more than my rhinestones!," McEntire wrote. "We sure have shared a lot of memories over the years and I'm looking forward to many more ahead of us. I can't imagine a world without Dolly."
"It was always my dream to be on the Opry," Parton says in her Opry member bio. "I actually got to sing on the Grand Ole Opry when I was about 10 years old. I became a member in the late '60s. They call it the 'Mother Church,' because the old Ryman was a church, but it's sacred to me, wherever it goes -- the church of my heart. For me, the Opry is like the song 'New York, New York' -- if you can make it there, you can make it anywhere."