Who would ever guess Justin Bieber and Selena Gomez are Phish heads in the making? The teen pop star couple and friends reportedly caught a Phish concert last night (Aug. 16) at a venue just outside of Los Angeles -- and seemed to end up having a blast, hanging backstage with the band and totally staying at the gig well past their scheduled departure time.

According to the Hollywood Reporter, the unexpected evening began at the behest of Bieber's guitarist and musical director Dan Kanter, who also happens to be a huge Phish fan. Kanter has been trying to get Bieber to take in the atmosphere of a Phish gig for years, and apparently Wednesday's show was the kind of opportunity Bieber just couldn't say no to.

Bieber dressed in a colorful tie-dye T-shirt and Philadelphia Flyers cap for the occasion, while his beau Gomez dressed down in a huge floppy hat. They spent the first set hanging by the soundboard and talking to longtime Phish lighting director Chris Kuroda, who apparently will be designing lights on Bieber's next tour -- so expect some totally trippy visuals next time around.

But it was intermission when the real fun stuff went down. That's when Bieber and Gomez made the pilgrimage backstage to meet frontman Trey Anastasio and the rest of Phish, posing for pictures with the band, crew and even the extended families of both.

Then it was back out for the second set, during which Bieber joined in the traditional glow stick wars that take place between fans. In fact, the couple and accompanying posse ended up sticking around through three-quarters of the set, when they were totally expected to bolt after intermission. Who knows, maybe next time Bieber will come out and sit in on 'Bouncing Around the Room.'