The group gave the U.S DJ permission to sample their 1996 hit for a new track after agreeing to reform last year (18).
The new tune, titled "Spicy", which also features Charli and French producer Herve Pagez, has been kept under wraps but users shared links to the track on the social media site Reddit earlier this month.
A source told British newspaper The Sun that the girls are disappointed with the leak, but happy that it seems to have been received well by fans ahead of a possible video release next week, end June 02.
"This song has been years in the making. It's really disappointing that it's been leaked at the last minute," the insider revealed. "But people who have heard it seem to be loving it, which is promising ahead of its release. Charli sings the verses and the chorus has been mashed up and turned on its head for a really cool dance song".
The new song does not feature the girls on vocals and their representatives previously told U.S. website Bustle that "there are no current plans for this (the remix) to be performed on tour".