The country music legend - who is in the middle of her 'Backwards Barbie' UK tour - is reportedly set to perform at the world famous three-day event on Sunday (29.06.08).
Organiser Emily Eavis revealed on Wednesday (25.06.08) a last-minute surprise guest was set to play - but refused to say who.
She told the official Glastonbury festival website: "We've just confirmed a really exciting last-minute surprise on The Park Stage, but we can't announce that yet."
The name had been kept under wraps until today's reports that the '9 to 5' singer is to play at the event which begins today (27.06.08).
Scottish rockers Franz Ferdinand are another last-minute addition to the bill. They will perform tonight on The Park Stage at around 10pm.
This year's Glastonbury festival, which takes place in Somerset, South West England, is headlined by rockers Kings of Leon, rap star Jay-Z and indie old-timers The Verve.
