Actor Gerard Butler thrilled diners when he joined a restaurant’s house band for an impromptu performance last weekend. Butler, 42, was enjoying a night-out with friends at Manhattan hotspot The Darby, when members of the venue’s music team asked him if he would care to sing. Butler obliged and delighted the crowd by singing tracks by The Rolling Stones and The Doors, reports nypost.com. “He had the entire restaurant singing. He killed it,” informs a source.