album, Rumours, in early 1976 and continued until late in the year. Also, Nicks and Buckingham sang back-up on Warren Zevon's eponymous second album. Among Nicks' contributions to Rumours was "Dreams", which became the band's only Billboard Hot 100 number-one hit single. Nicks had also written and recorded the song "Silver Springs", but it was not included on the album because the early versions of the song ran too long, and the band didn't want too many slow songs on the album. Studio engineer and co-producer Ken Caillat said that Nicks was very unhappy to find that the band had decided against her song "Silver Springs", which he said was beautifully crafted, and carried some of the band's best guitar work. "Silver Springs", written about her tumultuous relationship with Buckingham, was released as a B-side of the "Go Your Own Way" single—Buckingham's equally critical song about Nicks. Copies of the single eventually became collectors' items among fans of Fleetwood Mac. "Silver Springs" was included on the four-disc Fleetwood Mac retrospective 25 Years – The Chain in 1992. Rumours, Fleetwood Mac's second album after the incorporation of Nicks and Buckingham, was the best-selling album of 1977 and had sold over 45 million copies worldwide, making it one of the best selling albums of all time. The album remained at number one on the American albums chart for 31 weeks and reached number one in other countries. The album won the Grammy Award for Album of the Year in 1978. It produced four U.S. Billboard Hot 100 top-ten singles, with Nicks' "Dreams" being the band's only Billboard Hot 100 number-one hit. In November 1977, after a New Zealand concert on the Rumours tour, Nicks and Fleetwood secretly began an affair. Fleetwood was married to Jenny Boyd. "Never in a million years could you have told me that would happen," Nicks has stated. "Everybody was angry because Mick was married to a wonderful girl and had two wonderful children. I was horrified. I loved these people. I loved his family. So it couldn't possibly work out. And it didn't. I just couldn't." Nicks ended the affair soon after it began. She has stated that had the affair progressed, it "would have been the end of Fleetwood Mac". By October 1978, Mick Fleetwood left Boyd for Nicks' friend, Sara Recor. 1979–1982: Tusk and Mirage After the success of the Rumours album and tour in