Paul McCartney to replace Cobain in Nirvana gig

The sensational gig will see the surviving members of the grunge band together for the first time in 20 years and Paul will sing with them as they play a new song at a star-filled charity concert in New York, reported Sun online.

McCartney, 70, has been secretly working with Foo Fighters singer Dave Grohl and bassist Krist Novoselic after a recent session at a studio.

The pair were founding members of Nirvana along with Cobain, who committed suicide in 1994.

"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'. I couldn't believe it," McCartney said.