The king of nightmares himself, Alice Cooper, had a little surprise for theater fans who came out to see the production of ‘Rock of Ages’ in London Tuesday night (Aug. 14).

Cooper performed ‘School’s Out’ to the delight of those in attendance. The performance was a special one for Cooper, as the 40th anniversary of the song reaching the No. 1 slot on the charts in the U.K. had just passed.

Earlier in the week, there had been rumors that Cooper might stop by for a surprise performance, and Alice himself teased via Twitter, “Hearing that @rockofagesuk in London is GOOD. But worthy of me crashing their little show? I’LL BE THE JUDGE OF THAT!”

To top it off, Cooper added a clip to his tweet of his “We’re Not Worthy!” appearance in ‘Wayne’s World.,’ then spent much of the week leading up to the show tweeting some of the ‘Rock of Ages’ cast members.

Cooper is coming off the ‘No More Mr. Nice Guy’ tour, which broke several attendance records in the U.S. and Europe. The singer was in London to promote his upcoming ‘Night of Fear’ U.K. tour. One of the stops on the run will be on Halloween, and will make Cooper the only foreign artist to have played at London’s Wembley Stadium for five straight decades. Cooper will begin rehearsals for the new tour in early October.

Watch Alice Cooper Performing at London’s ‘Rock of Ages’