Mick Jagger and Tina Turner were friends long before they hooked up onstage in Philadelphia for Live Aid on July 13, 1985. It was a history that went back almost 20 years, when Turner, along with bandleader husband Ike and their group, toured England with the Rolling Stones in 1966.

They also brought the Turners with them on their historic 1969 tour, which included the chaotic Altamont show and the New York City gig that was the main source for the Stones' best-ever live album, Get Yer Ya-Yas Out! Jagger has even cited Turner as the inspiration for his moves.

But when she joined him onstage for two songs at Live Aid, both were solo artists: Jagger had released his first album without the Stones, She's the Boss, five months earlier, and Turner was in a career upswing after years of abuse and neglect from both her ex-husband and the record-buying public, with her comeback LP, Private Dancer, on its way to selling more than eight million copies worldwide.

In fact, Turner was probably a bigger star than Jagger when she made a surprise appearance for the final two numbers of his five-song Live Aid set. The Stones' most recent LP, 1983's Undercover, broke the band's eight-album No. 1 streak, which started back in 1971 with Sticky Fingers, by stalling at No. 4. Their next record, 1986's Dirty Work, also made it no higher than No. 4, and by that time, Jagger and Keith Richards' relationship was at an all-time low. (Richards and Ronnie Wood were at Live Aid too, playing with Bob Dylan during his acoustic set, which immediately followed Jagger's.)

So when Jagger started his brief Live Aid show late in the evening at JFK Stadium with two songs from She's the Boss -- "Lonely at the Top" and "Just Another Night" -- it was more out of shrugging curiosity than enthusiastic anticipation as far as most music fans were concerned. He threw in an obligatory Stones cut, "Miss You," following the pair of new solo numbers, and then invited Turner onstage to help him sing "State of Shock," the year-old Top 5 hit by the Jacksons on which Jagger made a guest appearance. (Incidentally, Michael Jackson, the biggest star on the planet at the time, was one of the few artists who did not participate in Live Aid, which also held a day-long show in London at the same time).

Watch Mick Jagger and Tina Turner Perform at Live Aid

Halfway through Jagger and Turner's six minutes together onstage, "State of Shock" gave way to "It's Only Rock 'N Roll (But I Like It)," which is hornier -- both literally and in the other sense -- than the Stones' original 1974 version of the song, as brass blasts and Jagger takes off his T-shirt and grinds against Turner.

By the end of the performance, he's pulled off her leather miniskirt, leaving the 45-year-old singer to finish the song in a black leotard and fishnet hose.

As far as spontaneous rock 'n' roll moments go, it's a rehearsed and calculated move -- a showmanship act worthy of both Jagger and Turner, two of the most electrifying and stage-hogging artists of the 20th century. But the audience, pumped after a day of goodwill (Live Aid was all about poverty relief, remember) and star after star after star onstage, ate it up. And in some ways, their performance stands as a highlight of the Philadelphia show.

Two years later, Jagger furthered his solo career with another album, Primitive Cool, which didn't even crack the Top 40, and then his first tour without the Stones, the seeds of which were planted during his 20-minute Live Aid set. Turner starred in Mad Max Beyond Thunderdome, which opened three days before her Live Aid appearance. The following year, she released Private Dancer's follow-up, Break Every Rule, another Top 5 hit and multi-platinum smash.