ZZ Top fans had reason to be disappointed this summer: The Rock and Roll Hall of Famers were supposed to play North Texas with Jimmy Buffet, a piña colada-fueled party. But alas, health issues forced the Houston-by-way-of-Dallas trio to drop out. Billy Gibbons, however, wound up hanging around Dallas anyway, popping into The Foundry for a friend's private birthday party. Lo and behold, Mr. Dark Sunglasses hopped onstage, too, jamming out with the Relatives on a rendition of his band's classic "La Grange." The magic moment might've been lost to the wider public if it hadn't been caught on video. Gibbons seemed to enjoy himself, too, popping up later that night for an after party at the nearby Belmont Hotel —but you actually had to be there for that one.