Buckingham and Nicks were dating at the time they joined Fleetwood Mac in 1974, but their romance ended just after the group's first album was released a year later.
The turmoil of their break-up inspired several songs on Rumours, which would become one of the biggest-selling albums of all time.
Buckingham explained that he and Nicks have repaired their relationship over time and are now very good friends.
"I've known [Stevie] since high school," he told The AP. "I spent some time with her when she was finishing up her solo album [In Your Dreams] and mine [Seeds We Sow] was already done.
"We worked on some stuff together and had some real quality time. And all these years later, that there's still some chapters to unfold with the two of us seems just to be the sweetest thing."
Buckingham also revealed that he enjoyed reuniting with Fleetwood Mac for their 2009 world tour.
He explained: "I keep feeling like the Fleetwood Mac experience... seems like it keeps getting better for me. That's just a reflection of how things have gotten better for me personally as a solo artist and just in my personal life, and I can bring all that back and appreciate all the nuances of Fleetwood Mac and add to the mix in a very communal and supportive way."
Buckingham recently suggested that Fleetwood Mac have no current plans to tour, but he suspects they will reunite again in the near future.
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Watch Fleetwood Mac perform 'The Chain' below: