Michael McDonald Didn't Meet Patti LaBelle Until After Their 1986 Duet 'On My Own' Was on the Radio (Exclusive)

Though Michael McDonald collaboration with Patti LaBelle came to be an unlikely fashion, he wouldn't have wanted it any other way.

In What a Fool Believes, out now, the longtime Doobie Brothers member leans in to his life motto: being open to the randomness of life. In the case of "On My Own," that's exactly what happened — and it turned out to be something greater than he ever imagined.

"I was telling [Patti] just the other night how it was so funny how we hadn't met. The song was recorded and it was out on the radio. We still hadn't met until we had to do The Tonight Show [months later]. That was the first time we actually met and did the song together," McDonald, 72, tells PEOPLE exclusively.

McDonald and LaBelle, 79, released "On My Own" in 1986 and at the time, they each recorded their parts individually. Now knowing her performance style, McDonald thinks it was for the best.

"Patti's such a formidable live performer and such an artist at improvisation. And that's pretty much her thing. I don't think she sings any song the same way twice," he says. "It's always in that moment that she's creating the melody and the feel of the song. And she's very good at it."

He adds, "Ad-libbing is not one of my favorite things because I don't know that I'm that good at it. But I was kind of happy I didn't have to go one-on-one with her in the studio and try to keep up with her at the microphone!"

After she recorded her part, McDonald shaped his "vocal around what she had already done" and he feels it was "a better use of my talent than trying to really bring it in the moment."

"I think in the end, it really gave me some ideas on how to sing the song with her at a later date," he says.

Fast forward to April of this year, the duo set sail together for a three-night headline R&B cruise and caught up like old friends.

"We sang, 'On My Own' together both nights. Although I had wished I was in a little better voice, I hadn't sung that much in a long time," he admits. "It was wonderful. She's in such great form, it's just amazing to hear her sing. She hasn't lost a thing and she was killing it."

"I almost broke and run on the first show. I was thinking, 'I don't know if I can go out there and hold up under the pressure.' But she was fantastic. It was wonderful to do that song with her a couple more times," he concludes.

Though McDonald has sang the song on his own over the years, he adds that singing it with LaBelle is a "special occasion every time for me."

"I always look forward to those moments," he says.

For more from McDonald, pick up the latest issue of PEOPLE, on newsstands everywhere now.