Last week, surviving Audioslave members posted video of themselves playing "Like A Stone" at a Prophets of Rage practice, in memory of Chris Cornell. Now we know at least one reason they were rehearsing it.

At their set at Germany's Rock Am Ring festival over the weekend, they brought out System of a Down frontman Serj Tankian to sing lead vocals on the song. Pro-shot video of the performance has been released, and Serj sounds pretty damn great singing that song. Watch below. Prophets of Rage also worked part of Audioslave's "Cochise" into the Rage Against the Machine song "Sleep Now in the Fire" during their Rock Am Ring set (full setlist below).

Prophets of Rage's upcoming festival appearances include the Ozzy-headlined Louder Than Life and Riot Fest.

As for System of a Down, they recently played some deep cuts live for the first time in years, including the first performance of "Pictures" in 17 years. The band are also very slowly working on a followup to 2005's Mesmerize/Hypnotize.