It was the reunion tour many people thought would never happen -- but now that the Stone Roses are back on the road, anything can happen, up to and including a surprise cameo from Lily Allen at the band's Saturday (June 30) show.

Allen walked onstage wearing a red Stone Roses shirt to perform 'Just Be Good to Green,' her 2010 single with rapper Professor Green (who joined her for the performance). Later, she joked about her performance on Twitter, telling followers "No @professorgreen wasnt swinging a cat around on stage @HEATONPARK that was me trying to sing. loved it , thanks manchester x x x."

Allen's return to the stage offered live proof of her intentions to return to music after proclaiming her retirement in 2009. Earlier this year, she was spotted outside a recording studio, sparking rumors that she was working on her first album since 2009's 'It's Not Me, It's You.'

More recently, Allen confirmed the rumors, telling Twitter followers that she was in the studio with producer Greg Kurstin "throwing s--- at the wall and seeing if anything sticks."

Meanwhile, the Stone Roses tour continues despite some occasional bumps in the road, with Reuters proclaiming Saturday's show "a triumph" and saying it "left hundreds of thousands of fans wanting more."

Watch Lily Allen Perform With Professor Green at Stone Roses Gig