Abba star Agnetha Faltskog stunned fans by hitting the stage for a surprise performance at a London charity concert on Tuesday (12Nov13), marking her first high-profile gig in 25 years. The Swedish singer, who has reportedly not performed in front of an audience for more than two decades, was the surprise guest at Gary Barlow's Children In Need Rocks concert, which was held at the city's Eventim Apollo venue. Faltskog performed her duet with Barlow, I should've Followed You Home, to raise cash for the BBC's annual Children In Need charity event, which supports underprivileged kids around the world. British girl band Little Mix and Barlow's former Take That co-star Robbie Williams also took to the stage to perform at the first of two charity concerts. The second gig will be held at the same venue on Wednesday (13Nov13) with performances from Ellie Goulding and Rizzle Kicks.