Alice Cooper and Marilyn Manson kicked off their co-headlining summer tour on Saturday (June 1), and it didn't take long for the two shock rock titans to come together for a duet.

Manson joined Cooper during his set, coming out on stage to join him for a rendition of 'I'm Eighteen' (embedded above). It marks the second time the duo has collaborated on Cooper's 1971 hit; they previously performed it together in July of 2007, when both artists traveled to Bucharest as part of the B'Estival lineup and shared the stage for 'I'm Eighteen' and 'Sweet Dreams (Are Made of This).'

As we previously reported, fans can expect to see Cooper and Manson make a habit of working together during their 'Monsters of Madness' tour; during a recent interview, he predicted, "It’s inevitable that we will end up doing something together … When you get these two sick brains together, you never know what’s going to show up on that stage."

Following the tour, Cooper plans to finish working on his next album, a collection of covers that he recently told Rolling Stone is "about halfway" finished. "The tour is sort of in the way, but that’s okay, because we don’t need to put the record out until next year," he pointed out. "I always tour June through December anyway, so we knew that was coming anyway, and this is one of those records we’re doing just for the fun of it, so if it comes out next year, no big deal."

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