Right before Anthrax took the stage at the Best Buy Theater in NYC last night, Slayer’s Kerry King, Anthrax’s Charlie Benante and Frank Bello, Megadeth’s David Ellefson, and Mike Portnoy took part in the second Metal Masters clinic. However, fans who attended the free clinic ended up being a part of a historical metal moment, as Philip Anselmo joined the musicians onstage to perform Pantera’s “A New Level” and “Fucking Hostile.”

Earlier in the day, both the former Pantera singer and Anthrax’s Scott Ian (who also took part in the Pantera encore) teased fans about the surprise appearance via Facebook and Twitter. In addition to the Metal Masters clinic performance, Anselmo also joined Anthrax onstage during “Indians” (joining towards the end to play an outro bass solo).

Fans who couldn’t be there in person had the chance to catch the metal all-star jam during Revolver’s live webcast stream. However, in case you missed the stream as well, you can watch clips of the performance online (until they’re taken down, that is). You can watch their cover of “A New Level” above, while their performance of “Fucking Hostile” can be seen after the jump. Stay tuned for our review of the Anthrax show shortly.