Britney Spears - Till The World Ends
The megastars finish their mega-collaboration, "Big Fat Bass" and Britney explains the meaning of Femme Fatale to Sway....
Spears hasn't performed live in over a year and needs to get comfortable with her dancers and the elaborate staging.
Britney Spears performs "Till the World Ends" for hundreds of adoring fans at Rain nightclub in Las Vegas.
Britney Spears (with some help from will.i.am) bangs around a "Big Fat Bass" in this online exclusive performance clip.