Saturday night (April 16) at Coachella was supposed to be all about Guns N' Roses' classic lineup reunion, but thanks to a special appearance from another metal icon, the evening turned into a shockingly great preview of the next chapter of a much older hard rock band.

Axl Rose to Tour With AC/DC

Just hours after AC/DC confirmed rumors that Axl Rose would serve as singer for the band's remaining tour dates after hearing issues forced vocalist Brian Johnson to take a step back from the band after 36 years, Rose hit the stage with his formerly estranged GnR compatriots Duff McKagan and Slash at Coachella. But even though there have only been a handful of GnR "classic lineup" reunion shows this year, the most jaw-dropping moment of the night wasn't centered around the trio back in action: It was a glimpse into Axl's next move.

Seated on his rock n' roll recovery throne (lent to him by Dave Grohl), Rose apologized to the crowd for not "running around" on stage as per usual. "I do feel bad about sitting here on my ass," Rose said. As a consolation prize, he offered to bring out a special guest to liven things up.

Many were undoubtedly expecting something along the lines of Sebastian Bach, who joined the band for a previous reunion gig. Instead, the crowd was pleasantly shocked to see AC/DC's Angus Young -- in full schoolboy uniform despite his 61 years -- take the stage with Guns N' Roses (surprise aside, the drummer's AC/DC t-shirt was a subtle harbinger things to come).

Guns N' Roses Eyeing $3 Million Per Reunion Show

While Rose was forced to remain seated throughout, Young did more than his fair share to make up for Axl's immobility by doing the Chuck Berry duck walk all around the stage while the GnR singer wailed and nailed the band's "Whole Lotta Rosie" and "Riff Raff" (both originally Bon Scott vocals). Anyone concerned that Rose isn't up for the towering task of speeding down the Aussie band's never-ending highway to hell need only listen to what happened at Coachella to have their fears assuaged.

Aside from the unexpected AC/DC detour, the proper Guns N' Roses show -- a small miracle in itself -- was a resounding success. There were no outright misfires -- sure, they sounded slightly out of sync on "Mr. Brownstone," and putting "Chinese Democracy" third wasn't the wisest pacing choice -- but there's no dismissing the experience of seeing a musical duo rekindle their strange magic together after such a long time apart. Slash's fingers flew over his frets like Muhammad Ali dancing in the boxing ring, and Rose brought an especially focused vocal performance to the stage on Saturday.

Forced to remain seated for the marathon concert, Rose looked like a caged animal at times -- and it suited him perfectly. Feeding off the satisfaction of GnR drawing a gargantuan crowd (it was much larger than the one LCD Soundsystem's reunion pulled in Friday night), Rose's gaze was tinged with a sort of sinister hunger. His eyes roamed the stage like an ailing, ravenous dog just waiting for the moment it's well enough to pounce.

And that day will come. Once his foot is healed and he's touring with his teenage heroes as their vocalist later this year, it looks like Axl Rose -- who for years seemed content to trudge through old Guns N' Roses hits like a pleasant but passionless day job -- may have his appetite for rock domination restored.