Members of SLAYER, MEGADETH and ANTHRAX joined METALLICA on stage earlier tonight (Tuesday, June 22) in Sofia, Bulgaria to perform the DIAMOND HEAD classic "Am I Evil?" METALLICA's James Hetfield, MEGADETH's Dave Mustaine and ANTHRAX's Joey Belladonna all took turns singing, with various other bandmembers playing guitar, bass and pounding on snare drums.

"After 29 years of doing this to reach this apex is just so fucking cool," tweeted ANTHRAX guitarist Scott Ian moments after the performance. "It was a monumental moment of epic proportions. I'm so high from the experience I can't sleep."

The last time Mustaine performed with METALLICA was on April 9, 1983 at the legendary Brooklyn, New York club L'Amour. He was unceremoniously fired by the band just weeks before they entered the studio to record their debut album, "Kill 'Em All", and was replaced by former EXODUS axeman Kirk Hammett.

Today's "Big Four" show, as part of the Sonisphere festival, will be beamed to more than 450 movie theatres in more than 140 markets in the U.S., along with cities in Europe, Canada and Latin America. In addition, it is being recorded for a forthcoming "Big Four" DVD.

The concert will be broadcast to theatres in high definition. Delayed screenings are planned for Australia, South Africa and New Zealand. 

METALLICA, SLAYER, MEGADETH and ANTHRAX — the so-called "Big Four" of 1980s thrash metal — played together for the first time in history last Wednesday night (June 16) in front of 81,000 fans at the Sonisphere festival at Bemowo Airport in Warsaw, Poland.