Mastodon (Kelliher second from left)

Bill Kelliher, guitarist for metal titans Mastodon, is currently being treated in London for an unidentified illness. He was admitted to the hospital November 3. "At this point all we know is that Bill was not feeling well upon arrival to the UK and went to the hospital where doctors are running tests now," a spokesperson tells SPIN.com.

The band have decided to continue as a trio on the European Unholy Alliance Chapter III Tour with Slayer, Trivium, and Amon Amarth. However, "doctors and Bill are hopeful that he will rejoin his band mates in time for their headlining tour of Europe, which begins Nov. 30 in Utrecht, Holland."

Get better Bill, we can't wait to hear that new material!