These lucky fans got to experience the rarest of the rare, when a legend fills in for another legend last-minute. Watch these 10 Epic Fill-In Performances!

Some bad blood between Ozzy Osbourne and Ronnie James Dio led to one of heavy metal’s greatest fill-in nights. Ozzy once decided to retire back in 1992, asking Black Sabbath to open for Ozzy Osbourne’s two farewell gigs. Dio refused to do it, claiming, “I’m not doing that. I’m not supporting a clown.” Tony Iommi was forced to improvise, leading the guitar icon to recruit Rob Halford, who had just left Judas Priest at the time. Halford sang Sabbath songs for two nights in Costa Mesa, Calif., giving fans a pair of phenomenal evenings.

When rumors started spreading that Axl Rose would be taking Brian Johnson’s vacant spot in AC/DC, most fans thought, “There’s no way in hell!” Strangely enough, it turned out to be true and Axl absolutely nailed it, leaving his critics in the dust. The Guns N’ Roses legend toured the world with AC/DC and now the question is how much longer Axl will front the band.

After Metallica drummer Lars Ulrich suffered a medical emergency right before his band’s performance at Download 2004, the thrashers were left with no anchor. To replace Ulrich, not one, but two legends manned the drum throne to allow Metallica to perform. After Dave Lombardo jammed two tracks with ’Tallica, Slipknot’s Joey Jordison saved the day by jamming eight songs behind the drums, effectively saving the gig.

Check out these 10 Epic Fill-In Performances in the Loud List above!

Watch More Loud Lists!

More From Loudwire