During the week, the Work singer uploaded photos of herself modelling a new look from her lingerie line Savage X Fenty.
Noticing her new post, Chris Brown left behind a "thirsty" comment that has left many of her fans less than thrilled, according to Fox News.
Captioning the photo: "Be the first to have this and more pieces from the @savagexfenty show now on SAVAGEX.com."
Only a few hours later and the 31-year-old's ex-boyfriend had wrote in the comments section: "I wanna be the lamp" (referencing a prop in the background) along with a smirking emoji face.
Rihanna's fans were quick to jump in and told the No Guidance singer to back off for his remark.
"Stay away from herrrr!!!!!" one person wrote. "You got somegod***n nerves," commented another person.
"Get out of here," wrote one individual, with another commenting, "Leave her alone".
The night before the 2009 Grammys, Rihanna was the victim of domestic violence when then-boyfriend Chris Brown assaulted her leaving her with visible contusions and bruises on her face.
Brown was sentenced to five years of probation and 180 days of community labour after pleading guilty to felony assault and making criminal threats.
This is the second time Chris Brown has been found lurking on his ex-girlfriend's social media. Last November, he left another comment under one of Rihanna's Instagram pictures, and her fans were not having it.