Lady Gaga was a headliner at Lollapalooza over the weekend, and tens of thousands of people jammed Chicago’s Grant Park to see her perform. But they might not have gotten the best Gaga show of the festival.

A few hours before she took the main stage on Friday (Aug. 6), Gaga made a surprise appearance on a side stage during the band Semi Precious Weapons’ set. Or, rather, on a stage and in the crowd.

]]>Justin Tranter, just for good measure, and he joined her in the crowd as well. From the video, it looks like the SPW set drew a pretty big crowd — several thousand, probably. We’re guessing, though, that many, many more will claim they were there. Follow Zap2it and Zap2itRick on Twitter and Zap2it on Facebook for the latest TV, movie and celebrity news.