This one almost defies explanation. Bruce Springsteen was rocking out to 76,000-plus thrilled spectators in London’s Hyde Park, a venue he’d wanted to play for 50 years, when he was joined by Paul McCartney. Then things got weird. Someone cut the microphones of perhaps the two greatest rock stars on the planet.

At 10:40 p.m. local time, as Springsteen and McCartney were winding up the extended "Twist and Shout," the sound suddenly dampened, and went quiet.

At first, the Boss didn't seem to notice. He attempted to address the crowd, apparently unaware that they couldn't hear him. But as it became clear that there was no amplification, he and lead guitarist Stevie Van Zandt played what looked to be a brief a cappella goodnight for the benefit of the front rows, shrugged, and left the stage.

That’s quite the ballsy move. Stupid, but ballsy nonetheless.

London's Westminster Council confirmed that concert organizers Hard Rock Calling had cut the power, saying they "were sticking to their license for the event." According to the Hard Rock Calling website, Springsteen had been due to finish his set at 10:15 p.m.

Van Zandt tweeted later, "I'm sorry but I have to be honest I'm pissed ... It didn't ruin the great night. But when I'm jamming with McCartney don't bug me!" He also implied his fans were denied their final number, saying, "We would have been off by 11 if we'd done one more."

A spokesman for concert operator Live Nation said: "It was unfortunate that the three hour plus performance by Bruce Springsteen was stopped right at the very end but the curfew is laid down by the authorities in the interest of the public's health and safety. Road closures around Hyde Park are put in place at specific times to make sure everyone can exit the area safely."