Mick Jagger, as it turns out, became Carly Simon's backup singer on "You're So Vain" because he just happened to pop into the studio the day of recording. The bad news is, that put him on the list of candidates that people think Simon's singing about.

Before they were famous, lots of artists sang backup for other artists. But once in awhile, they'll lend their talent to someone else because it's fun, or because they owe someone a favor or maybe just because they were asked to.

This week, we're going to listen in on a bunch of songs that have famous people singing backups. Some of them are pretty well known; others may come as a surprise to you.

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