Johnny Depp w/Alice Cooper in June, 2011; Christie Goodwin/Getty ImagesHollywood Vampires, the band formed by Alice Cooper and actor Johnny Depp, didn’t start out as the star-studded project it became.

“I had already written a bunch of music and we started recording and then it became this Vampire thing,” Depp said, explaining the origins of the project on Jimmy Kimmel Live! Thursday night.

Pretty soon, and apparently to Depp’s surprise, Cooper started bringing in a string of superstar performers to participate in the tribute to the original “Hollywood Vampires” — an informal group of rock stars who Cooper used to drink with in Los Angeles in the 1970s.

“It was pretty shocking,” Depp admitted of working with the likes of Aerosmith‘s Joe Perry, Joe Walsh and Paul McCartney.

Hanging around with Perry also had a side benefit for Depp beyond music. Depp is starring in Black Mass, out September 18, a movie in which he plays Boston gangster Whitey Bulger and, he said, Perry helped him with the part, if unintentionally. “Joe’s got a pretty thick Boston accent,” Depp told Kimmel. “So I just sponged it.”

“Wow: so there’s a little bit of Joe Perry in Whitey Bulger,” Kimmel said. “There is indeed, you know,” Depp laughed.

Hollywood Vampires, with Cooper, Depp, Perry and two ex-Guns N’ Roses members — bassist Duff McKagan and drummer Matt Sorum — as well as Cooper’s touring guitarist Tommy Henrickson and longtime Depp collaborator Bruce Witkin on piano and guitar, will play their first U.S. shows September 16 and 17at the famed Sunset Strip venue The Roxy Theatre in West Hollywood, California.

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