The Can’t Take My Eyes Off You singer told fans at the Cheltenham Literature Festival that organiser Michael Eavis had booked him to perform at the 2010 music event, which marks the 40th anniversary of the world-famous festival.
Tickets for the event, which takes place at Worthy Farm, Somerset, South West England, sold out in less than 24 hours of going on sale, despite no line-up announcements being made.
Veteran rockers The Rolling Stones are favourites to headline the final night of the three-day event, while U2, Radiohead and Beyonce Knowles are also being tipped to appear.
Organiser Eavis said: The expectations are really high. We’re trying to get the best headliners in the world.
Williams, 82, could even be joined at the festival by a special guest, after recently revealing he wants to perform with Robbie Williams.
He said: "I'd love to do a duet with Robbie - I'd do it in a second. I've covered his She's The One and although I haven't seen Robbie perform, I hear he's very good. Robbie is extremely talented.
