It's been a long time since Britney Spears performed live--but sources tell that the pop star will take the stage at the Billboard Music Awards in Las Vegas this Sunday.

Spears is set to perform twice. She'll first join Rihanna on stage to perform hit song 'S&M' and then appear with Nicki Minaj for a remix of Spears' hit 'Till the World Ends.' It will be the first time ever Spears performs with Minaj.

"It's gonna be big," a source told UsMagazine about the planned performances. "People will definitely be talking about it the next day."

The 2011 Billboard Music Awards air Sunday night at 8:00pm ET on ABC.