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CSS played the Other Stage on the Saturday at last year's festival, but their set was hindered by rainy weather.
Eavis claimed the band would be "amazing" on the smaller stage.
She told eFestivals: "They're one of the greatest party bands around and it's gonna be amazing seeing them up there on the Park's stage with its flaming Roman columns either side!
"We also have some really special surprises lined up for this year's festival, which we will not announce and will do our absolute best to keep secret! You'll have to trust us for the time being - but they're gonna be incredible!"
Kings of Leon, Jay-Z and The Verve have already been confirmed as this year's Glastonbury headliners.
Glastonbury Festival 2008 takes place on June 27-29.
