On June 15, 2011, Metallica announced that recording sessions with singer-songwriter Lou Reed had concluded. The album, which was titled "Lulu", was recorded over several months and comprised ten songs based on Frank Wedekind's "Lulu" plays "Earth Spirit" and "Pandora's Box". The album was released on October 31, 2011. The recording of the album was problematic at times; Lars Ulrich later said Lou Reed challenged him to a "street fight". On October 16, 2011, Robert Trujillo confirmed that the band was back in the studio and writing new material. He said, "The writing process for the new Metallica album has begun. We've been in the studio with Rick Rubin, working on a couple of things, and we're going to be recording during the most of next year."