Mike Wass Disbelief colors Kim Petras’ voice when asked about her reaction to the global success of “Unholy.” After searching for the right words, she lands on “fever dream.” While the reality of having the biggest song in the world might not have sunk in yet, the numbers don’t lie. In addition to being No. 1 on Billboard’s Global 200, the unapologetic collaboration with Sam Smith has topped the charts in multiple countries including the U.K., Australia, and Canada, and is looking to do the same in the U.S. — looming large at No. 2 on the Hot 100. While “Unholy” seemingly blew up overnight, it was actually five years in the making. “Sam reached out pretty early in my career,” the German pop star explains in her lightly accented English. As a fan, she was eager to make it happen, but the right song never came along until Smith sent her a demo of “Unholy.” “I knew I could add something special to it,” Petras says. “A week later, we were in the studio drinking whiskey and coming up with slutty lyrics.”