Stone Sour are undergoing yet another lineup change, as the band has officially parted ways with bassist Shawn Economaki.

Guitarist Jim Root let fans in on the news by posting an Instagram photo of the band performing with a new “mystery” bassist and writing, “Shawn is no longer with us. A lot has happened in the past year. We need to move forward and [there will] be more detail when the time is right. He’s still a great friend and we’re in touch. But for now we have a mystery dude that shreds filling in for the studio.”

Singer Corey Taylor reiterated via Twitter, “As some of you might have heard, but I’ll confirm it: Shawn Economaki is no longer with Stone Sour. We wish him luck in the future.”

Economaki split from the band last spring in the midst of a difficult stint on the Avalanche Tour, which also saw the band having to find a temporary fill-in for drummer Roy Mayorga, who was recovering from a mini-stroke. At the time, it was stated that Economaki was taking time away to deal with “personal issues.”

Stone Sour are in the process of working on their fourth disc, an album that Taylor told us in an exclusive interview was going to be a “grand” concept record. The band is currently recording just outside of Taylor and Root’s home base of Des Moines, Iowa with producer David Bottrill. While official details have yet to be announced, it is believed that the collection will be a double-disc set. Work on the project is expected to be completed by the time Taylor and Root leave for the Rockstar Energy Drink Mayhem Festival with their other band, Slipknot.