The singer will feature on a song from the rapper's new solo album #willpower, which is slated for release on September 24.
According to a handful of fans who attended the playback, the song is "dark" and "super sexy" and contains dubstep influences, reports Breathe Heavy.
Lyrics apparently include: "Bass thumpin' through my veins ... Gettin' sexy in this club / Lookin' sexy with some bub."
will.i.am also confirmed that he has collaborated with Justin Bieber, Chris Brown and Nicole Scherzinger for his new album.
Listen to Britney Spears and will.i.am's previous collaboration 'Big Fat Bass' below: