Coldplay frontman Chris Martin disguised himself as a skeleton to help Win Butler DJ at an Arcade Fire show at London's Roundhouse earlier this month, NME reports. In an interview with BBC Radio Two, Butler revealed that Martin had donned fancy dress to provide some undercover assistance in the DJ booth and described the Coldplay singer as an "amazing hype man." Speaking about the gig, for which fans were asked to attend in either formal wear or fancy dress, Butler said: "He [Martin] was out at the DJ booth with me the other night wearing a skull mask. It was pretty cool. He was the hype man, he's an amazing hype man." Asked by host Jo Whiley if anyone had recognised the singer, meanwhile, he replied: "I don't think so." Butler also hinted that the band would return to the UK for festivals next summer, which he described as always being a "special experience." Asked if he could give any hints as to which events they might play, he simply said: "Get your wellies ready" and then revealed that he had recently bought his six-month-old son his first pair of wellington boots in preparation for the UK festival season. Earlier today, Arcade Fire revealed that they were issuing a dress code for their US arena tour next year. Butler had previously told fans at the Roundhouse that he was not apologetic for making formal of fancy dress mandatory for their UK gigs, announcing to the crowd: "To anyone who felt uncomfortable dressing up - I'm not sorry," said Butler. "At least 70 percent of you are getting laid tonight ... As long as you showered. That's the secret. Boys."