*Rihanna promised a “shocking” addition to the remix of her track “Birthday Cake.”

According to gossip maven Miss Info, the addition is none other than her ex-boyfriend Chris Brown – who just last week was ordered to remain on supervised probation for assaulting her in 2009.

Producers say the song will be released this week.

Miss Info reported:

Your girl Info confirmed with two independent sources that Rihanna has Chris Brown featured on the song. He recorded both a singing verse, and a rap verse. (We’ll see if both of those verses make the final song.)

And as for rumors that Chris Brown attended Rihanna’s early birthday celebration after the Grammys this past weekend….Yes, that is also true. In fact, Chris arrived at the party with Rihanna. And stayed. It was not a drive-by appearance. And the energy between the two did not appear purely platonic. The party was a small intimate one. Family members, friends, and interestingly enough, management (Hov was not there, obviously). I imagine there were lots of mixed reactions in the room. (And no, everyone didn’t sign a confidentiality agreement.)

Speaking of confidentiality agreements, here’s how that went down, according to TMZ:

Chris Brown was so paranoid about keeping his attendance at Rihanna’s birthday party a big fat secret — he actually tried to FORCE partygoers to sign confidentiality agreements.

Sources tell us, Chris refused to enter the private party Monday night at the famous Hearst Mansion in Beverly Hills until everyone signed an NDA — sending his henchmen in beforehand to gather every partygoer’s signature.

Once they were all signed — most of them at least — we’re told Chris walked in … and spent a huge chunk of the night nuzzling up against Rihanna.

According to sources, the two got real intimate — sitting next to each other, even holding hands.

As for the rest of the party — we’re told it was jam-packed with celebs including Katy Perry, Bruno Mars, and Chris Martin (no Gwyneth).

In case you’re wondering about the b-day girl’s actual birthday cake, take a look below. It’s a big ol’ spliff  with a small Rihanna made out of icing, riding it like a horse.

rihanna b-day cake