Trooper, the Iron Maiden-themed ale, has reportedly sold more than 3.5 million pints since its launch in March 2013. Remarkably, the Cheshire, U.K.-based Robinsons Brewery has reached this number without spending so much as a thin 10 pence on advertising.

The smash-hit collaboration between the band and Robinsons began in the spring of 2012, according to the Publican's Morning Advertiser. But this wasn't simply a case of a band putting its name on a product. Maiden's Bruce Dickinson selected the beer's hops himself, after a blind tasting.

"I'm a lifelong fan of traditional English ale," Dickinson said, via the beer's website. "I thought I'd died and gone to heaven when we were asked to create our own beer. I have to say that I was very nervous: Robinsons are the only people I have had to audition for in 30 years. Their magic has been to create the alchemical wedding of flavor and texture that is Trooper."

Robinsons director of marketing David Bremner unveiled the Trooper stats at the Publican's Beer Innovation Summit. He said sales are up some eight percent in pubs across the U.K. Robinsons has since been approached about a similar beer partnership with Motorhead, but declined. "Bruce is considered knowledgeable and fanatical about beer," Bremner said. "So there was a truly authentic relationship."

Iron Maiden will conclude their 2014 tour of England with an appearance at Sonisphere this summer.

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