Emmylou Harris claims she had a hidden agenda when she recorded Dolly Parton’s “Coat of Many Colors” for her 1975 album Pieces of the Sky.

“When I made my record, Linda [Ronstadt] and I had told each other our favorite singer was Dolly,” Harris recalls. “I thought if I recorded a song of Dolly’s I would get to meet her, and I did the first time I went to Nashville.”

“I was as thrilled as you were,” Parton says.

Both Parton and Harris are seated at a long table at the United Methodist Communications office in Nashville for a media day to promote the newly remastered The Complete Trio Collection, due Sept. 9.

Harris’s outfit of jeans, silver boots and purple top with an embroidered scarf offsets Parton’s black blazer and fringe with peep toe booties. An altar with a wooden cross and an upright Baldwin piano flank the table as a small gathering of press sits on the edge of their seats for questions. The pressure was palpable to chronicle more than 40 years of musical friendship.

The memory of the first time they sang together with Ronstadt came back as if it was yesterday. It was in the early ‘70s when the three ladies first met over a girls’ night at Harris’s place in Los Angeles. That evening, they bonded instantly by singing classic country by the Louvin Brothers and the Carter Family.

“I called Linda and said, ‘Dolly’s coming over to my house,’” Harris says. “So she got in her little sports car and zipped over. We were delighted to meet each other. It was great. But of course, we were going to sing.”

“I didn’t really know all they knew because I was just getting to know them,” Parton says. “It was just one of those things where you’re like, ‘Oh! What is that sound?’ Even though you know it’s coming out of you, it was just such an amazing thing.”

Both Parton and Harris believe performing with Ronstadt brings out the best in each of the three music legends.

“It’s a wonderful feeling to just jump into these other voices that you love so much,” Harris says. “The three voices create a fourth voice in a way. … That was another part of the joy. It wasn’t work. You just opened your mouth and sang. After we figured out what songs we wanted to sing, who was going to sing which part, it was just a matter of getting the best version of it in the studio.”

CMT Hot 20 Countdown will spotlight the 40th anniversary of their first public performance together on Parton’s syndicated TV series, Dolly. The all-new Hot 20 airs Saturday (May 21) at 9 a.m. ET and re-airs Sunday (May 22).