Paul McCartney has some big shoes to fill, as he will be subbing for the late Kurt Cobain when Nirvana reunites on Wednesday.
The Beatles star will be performing with Dave Grohl and Krist Novoselic at the 12-12-12 concert being held to benefit victims of Superstorm Sandy.
The 70-year-old was asked to join the pair onstage by Grohl.
But he has admitted that at first, he didn’t quite register what it meant.
He told The Sun: ‘I didn't really know who they were. They are saying how good it is to be back together.
‘I said, “Whoa? You guys haven't played together for all that time?” And somebody whispered to me, “That's Nirvana. You're Kurt.”’
He added: ‘I couldn't believe it.’
The publication reports that the trio have been rehearsing in secret ahead of the benefit.
It is not the first time McCartney and Grohl have joined forces – they performed together at the 2012 Grammy Awards back in February.
McCartney led an Abbey Road medley as the finale for the ceremony and along with Grohl was joined by Bruce Springsteen and Joe Walsh of the Eagles.
Meanwhile, the relief concert, taking place at Madison Square Garden on Wednesday evening, is set to be even more star-studded.
Performances are expected from the likes of The Rolling Stones, The Who, Jon Bon Jovi, Kanye West, Billy Joel, Alicia Keys, Eric Clapton, and Roger Waters.
Producers are estimating that the show could rake in a staggering two billion viewers.
Nirvana split in 1994 after frontman Cobain tragically committed suicide.