Rihanna and Chris Brown to Collaborate on "Birthday Cake" Remix?!

Chris Brown was apparently on hand at Rihanna's birthday party to see her receive a cake shaped like a topless likeness of herself riding a giant spliff.

Now they're rumored to be collaborating on a remix of her song "Birthday Cake."

Seriously. New reports have been flying that Chris Brown, of all people, is the mystery collaborator on a soon-to-drop remix of Rihanna's quick-hit song.

Surprising, and probably disappointing for some of her fans, but not as absurd a concept as it once seemed, given that they've grown close again.

"They can say whatever, Ima do whatever, No pain is forever," Rihanna tweeted Friday morning, quoting her hit song "Hard." "YUP! YOU KNOW THIS."

Cryptic. Or just catchy. That song was good.

Neither side is commenting about the rumored collaboration, but a full-length version of Rihanna's minute-long track (above) has long been in the works.

"It's gonna be crazy," producing team Da Internz told MTV News last week regarding the tune. "And the feature on there is gonna shock the world."

Could that mean what we think it means?

They even said a clip or some other visual tease would be dropping, too: "The visual has to go with it 'cause everybody's going to be like, 'Oh my god!'"

Brown was recently spotted leaving the same Hollywood recording studio as Rihanna amid reports that they're keeping increasingly close company.

It's unclear exactly when and if the single will drop (apart from soon), though if true, the once-smoking-hot pair certainly opted for some curious timing.

Chris, who just released his latest video, for "Turn Up the Music" (above) has seen people turn up the heat on him ever since Sunday night's Grammys.

It was three years ago this month that Brown was arrested after brutally beating Rihanna while in the car leaving a party on the eve of the Grammys.

With that in mind, many celebs and fans alike criticized the award show for giving him such a platform to perform (and win), which he was upset about.

Chris not only attended Rihanna's birthday bash Monday, but went so far as to demand all partygoers sign a NDA to prevent word from leaking out.

Clearly that didn't work out.

The singer was also forced to deny a report earlier this week that he attempted to pick up a girl by using the line, "I promise I won't beat you."

Additionally, Brown has been fortifying himself against both peer and media criticism in recent days, tweeting and deleting aggressive missives.

Perhaps he's bracing for more backlash? A duet with Rihanna would certainly bring that - probably tenfold compared to what he's endured this week.