Stone Sour have announced that former Dream Theater drummer Mike Portnoy will be joining them behind the kit, subbing in for the group's regular drummer Roy Mayorga, for a one-off upcoming show at the world-renowned Rock In Rio Festival on September 24.

Said Portnoy: “It's my honor and pleasure to be able to help out my good friends in Stone Sour and my brother Roy in their time of need.  It's also an unexpected treat for me to get another visit with some of the greatest fans in the world down in Brazil.”

Stone Sour and Slipknot frontman Corey Taylor said, “We've been waiting a long time for the opportunity to come to South America. This year's Rock in Rio should be fantastic. With Roy expecting his first child, we'll charge on without him, but having Mike fill in for this one show will be great. We can't wait to take the stage and lay it down the only way Stone Sour knows how: full on and in your face!"

Stone Sour is currently conceptualizing a special EP/DVD release for this winter, along with a special MP3 giveaway via their Facebook page. Stay tuned for full details soon.