Metallica fans despair: The band looks to have lost 250 riffs.

Their guitarist Kirk Hammett said in 2012 he'd come up with some 400 riffs for the band's forthcoming 10th album but he's just admitted 250 of them were recorded to a smartphone he lost six months ago.

“I put riffs on my iPhone, but something very unfortunate happened to me about six months ago," he told Hatebreed frontman Jamey Jasta in an interview transcribed by Blabbermouth.

"I lost my iPhone [containing] 250 musical ideas. And I was crushed. It didn’t get backed up.”

Although Hammett thinks "it still might turn up," that sounds unlikely - and he says he can only remember about eight of them.

Nevertheless, he said that the new album is "super riffy, super heavy" and is starting to sound a lot like 2008's Death Magnetic while also reminding him of ...And Justice For All from 1988.

While he gets back to the fretboard drawing board we've got one word for him: iCloud.