Last weekend, producing duo Da Internz got the Internet buzzing when they told MTV News that the featured performer on Rihanna's upcoming remix to "Birthday Cake" would "shock the world," a phrase that immediately stoked speculation that the collaborator would be Chris Brown. Brown and Rihanna will forever be known for the incident three years ago where he beat her on the weekend of the Grammys, but recently, the singers have been spied several times in close company — in fact, TMZ says that Brown showed up at Rihanna's birthday party last night and tried to have his fellow guests sign confidentiality agreements — and a widely circulated report from Miss Info cites sources who claim that Brown is indeed the "Birthday Cake" performer, and that he's already recorded two verses for the remix. Still, some speculate that the guest will actually be Christina Aguilera, since Rihanna once tweeted, "I need somebody #DIRRRTY on my Birthday #CAKE." Expect an answer soon, and in the meantime, enjoy Rihanna's actual birthday cake: a confection shaped like the singer riding a giant spliff that she served guests at her party. Kids!