The Beatles legend
sent fans into a tailspin on Monday when he dropped heavy hints that he would be performing at the festival, sharing an image on his Twitter page featuring Philip Glass, Emma Stone and Chuck Berry.
The black and white snap led many to link together the stars' surnames to spell out Glass-Stone-Berry, or Glastonbury.
A few hours later, Eavis, whose father Michael set up the festival in 1970, confirmed one of the worst-kept secrets in pop: McCartney will be headlining at Glastonbury's 50th anniversary next year.
Posting on Twitter
and Instagram, Eavis said: "IT'S REAL!! So excited.. Having Paul McCartney coming back to headline the Pyramid next year is an absolute dream come true."
"There really was no one that we wanted more for the 50th anniversary," she added.
There were rumors the 77-year-old musician might take to the Pyramid Stage next year ever since festival co-organizer Michael Eavis said he was hopeful McCartney would play at the event.
In September, McCartney said in a Radio 2 interview: "People are saying that it will be good if I did it, so I'm starting to think about whether I can or whether it would be a good thing ... It's starting to become some remote kind of possibility."
McCartney previously headlined Glastonbury in 2004, when he played a 33-song set spanning the Beatles, Wings and his solo material, including two encores.
The former Supremes star will play the Pyramid Stage on Sunday, June 28, on the final day of the five-day event in Somerset, England.
Tickets for next year's festival sold out in little more than half an hour. Emily Eavis said on Twitter that 2.4 million people had registered online for the chance to buy tickets costing £265 (around $340) each.