The Rolling Stones were joined onstage by Eric Clapton last night, November 29, in the second of two London O2 Arena shows celebrating the band's 50th anniversary. Following in the footsteps of fellow guitar great Jeff Beck, who performed with the Stones Sunday night, Clapton joined the band to rip through another blues standard, Muddy Waters' "Champagne & Reefer," which the band also performed with Buddy Guy several years ago.