It has just been reported that R&B superstar Whitney Houston passed away today (Feb. 11) at the age of 48. Details are unclear right now, but she was apparently found dead at the Beverly Hilton hotel. With this shocking news, people in the music industry and fans around the world are stunned. Members of the rock and metal communities are no exception, as such artists as Lamb of God, Nickelback, Guns N' Roses, Disturbed singer David Draiman, Slash and more have reacted via Twitter. Below is a list of Tweets from rock acts, with some simply breaking the news to their followers and others expressing condolences at the news. We will update the list as more rock and metal artists react on Twitter.