Someone better remind Guns n' Roses where Slane Castle is following a boo boo by the band at a gig in Australia.

The reformed band, who are due to play a sold-out show at Slane on May 27, had a real-life Spinal Tap moment on Tuesday and have apologised to their Australian fans after shouting "Hello, Sydney!" when they stepped on stage in Melbourne. 

The blunder was met with boos from the audience, after the band reportedly arrived late for the show at Melbourne Cricket Ground. 

Shortly after, Guns N' Roses posted on Twitter: "Melbourne! Accidentally after 30 years McBob made an error, we're truly sorry. Thank you for coming out tonight!"

Guitar technician McBob has been introducing the group on to stages around the world during their latest shows.

The Melbourne show followed two gigs in Sydney over the weekend as part of Guns N' Roses' ongoing global Not In This Lifetime tour, which features founding members Axl Rose, Slash and Duff McKagan.

Fans have already shown appreciation for the group's public apology on social media.

One follower replied to the post on Twitter with: "One mistake every 30 years... Reasonable."

Another added: "As long as he shouts 'Birmingham!' when you're in London this summer, all is forgiven."

Guns N' Roses make their return to Slane Castle this May, the first time they've played the iconic Meath venue since 1992. Tickets for the show went on sale last December and 80,000 tickets were snapped up within a day.

The band's 35-date Not in This Lifetime tour sold one million tickets across Irish, European and Canadian dates after going on sale, with the tour selling three million tickets in total last year, making it the year's most successful rock tour..