Midway through Megadeth's set on June 11 at the Download Fesitval in Donington, England, they brought out a fellow survivor of the Los Angeles metal scene of the '80s: Nikki Sixx joined them onstage to play bass and sing background vocals on a cover of the Sex Pistols' "Anarchy in the U.K." You can watch the video above.

Eon Music notes that Dave Mustaine introduced Sixx, who played earlier in the day with Sixx:A.M., by acknowledging the not-too-pleasant history between Megadeth and Motley Crue. "Back when Megadeth were starting out, we lived in L.A., and there was a lot of rivalry between the big bands,” he said, before pivoting to a more positive "with this guest, it’s a coming-in together of both sides.” Following the performance, Mustaine added, "Well, hell has frozen over, hasn’t it?”

While the two acts may have had their differences in the old days, there was common ground in their choice of song. "Anarchy in the U.K." is one of punk's most defining anthems, but both Megadeth and Sixx have a history with it. Megadeth recorded it for 1988's So Far, So Good ... So What!, while Motley Crue's version appeared as a new track on their 1991 compilation Decade of Decadence 81-91.

Sixx:A.M. are touring behind Prayers for the Damned Vol. 1, the first of two albums they plan to release this year. And even though Sixx has said that they "never will play Motley Crue music," last week the group performed the Crue's "Live Wire" while visiting the French radio show La Bande Originale de Nagui.

See Motley Crue and Other Rockers in the Top 100 Albums of the '80s