The singer is joining the likes of Sir Elton John, Lily Allen and Take That for the tenth anniversary gig at Wembley Stadium.
She said: "She was lovely so its kind of nice to do it and its nice that they want me to do it."
There's less than a week to go but Ms Stone hasn't yet 100 per cent decided her set list, she has had suggestions put to her though by none other than Prince William.
The Prince himself felt it was an important way of marking the death of Diana ten years on.
He added: "We wanted to have this big concert, full of energy, full of the sort of fun and happiness which I know she would have wanted. And on her birthday as well, it's got to be the best birthday present she ever had."