Chris Brown rapped a new un-released song alongside Rihanna at a party for P.Diddy earlier this week.

At Hollywood's Supper Club on Wednesday, Brown rapped in front of an audience that included Ne-Yo and Red Café, among others.

While Rihanna didn't sing during the impromptu performance, the two are working together on their second single, a rep for Brown confirmed to E! News last month.

There's no hint as to what the song will be about, but based on previous collaborations, it will likely be about their tumultuous relationship.

Brown and Rihanna have previously worked together on "Nobodies Business," which was featured on her seventh studio album, "Unapologetic."

They also did the hit single, "Umbrella," and then remixed each other’s singles, Rihanna’s "Birthday Cake," and Brown’s "Turn Up The Music."

The high-profile couple caused controversy when she featured him on the remix of "Birthday Cake." On the track, Brown sang, "Girl I wanna [expletive] you right now. Been a long time. I’ve been missing your body. Let me turn the lights down. When the window go down, it's a private party."

Rihanna also performed on Brown's song, "Turn Up the Music." She crooned, “"Turn up the music cause I feel a little turned on/ Turn on the music, don't you try to turn me down." She later added, “I love you baby.”

In 2009, Brown assaulted Rihanna, hitting her so forcefully that she had major contusions on her face, a split lip, and a bloody nose.

He eventually pleaded guilty to assault and was ordered to stay away from her until 2011.

Since then, they've rekindled their romance.