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Green Day's Billie Joe Armstrong played a bit of a replacement himself during the Replacement's set at Coachella this weekend. 

Billboard says the rocker took the stage with the iconic alt-rockers Friday night to help an ailing Paul Westerberg with the guitar parts.  Westerberg was plagued by back trouble, and spent much of the set singing and playing from a sofa.  He joked that Armstrong was an "expansion" of the band, which the Green Day leader and longtime Replacements fan called a dream come true. 

The Replacements' performance was part of the opening day of Coachella's second weekend.  Other performers at the festival in Indio, California included OutKast, Muse, Queens of the Stone Age, Arcade Fire, and more. 

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