Britney will do one performance -- potentially the opening number -- with Rihanna, 23. The duo will perform Rihanna's hit song "S&M."
Spears will also be performing for the first time ever with Nicki Minaj, 26. Spears and Minaj will partner up for a remix of Spears' hit "Till The World Ends."
"I'm obviously honored to be out with Britney," Nicki Minaj tells Us of the tour. "She's freakin' paved the way for so many things right now in pop culture. I'm excited to be on with her."
"It's gonna be big," a source says of the Billboard performance. "People will definitely be talking about it the next day."
The 2011 Billboard Music Awards air Sunday night at 8:00 p.m. on ABC.