Mayhem Festival 2015 included a Danish heavy metal musician who was the lead vocalist for what non-namesake band?
Mayhem Festival 2015:  It was confirmed that Slayer, King Diamond, Hellyeah and The Devil Wears Prada will be headlining the festival, while Whitechapel, Thy Art Is Murder, Jungle Rot and Sister Sin would be among those supporting. King Diamond: Kim Bendix Petersen (born 14 June 1956), better known by his stage name King Diamond, is a Danish heavy metal musician. King Diamond:  He is the lead vocalist for both Mercyful Fate and the eponymous King Diamond.
Mercyful Fate