The fans who showed up for the Aerosmith/Slash concert in Gorge, WA, on Aug. 16 received a memorable surprise during Slash's set.

As you can see in the fan-shot, front-row footage above, Slash was joined by his former Guns N' Roses bandmate Duff McKagan for a performance of the GNR song 'It's So Easy.'

Originally recorded for the band's 1987 debut album 'Appetite for Destruction,' the song served as an early European single in the months before the album started taking off, and has remained a live set-list staple for the current incarnation of GNR, as well as for McKagan's band Loaded -- and it was also a concert favorite for Velvet Revolver, the now-on-hiatus group McKagan and Slash started with singer Scott Weiland and former GNR drummer Matt Sorum.

McKagan and Slash's onstage reunion comes a couple of months after McKagan's much-publicized appearances with the current Guns N' Roses lineup, which found him pinch-hitting for bassist Tommy Stinson while Stinson fulfilled some Replacements commitments. At the time, Slash shrugged off questions about whether McKagan taking the stage with Axl Rose bothered him, and he obviously meant it.

It's great to see these guys playing together again, but it may not happen again for awhile: McKagan's made it clear that Velvet Revolver have had their troubles finding a replacement for Weiland, and with a new solo album just over the horizon, Slash will be busy for the foreseeable future.