Rihanna back with Chris Brown?

Rihanna and her ex-boyfriend Chris Brown have allegedly been secretly hooking up.

The 24-year-old pop beauty collaborated with the R&B star - who was convicted for assaulting the 'Russian Roulette' hitmaker in 2009 - on her latest single 'Birthday Cake' and the pair have reportedly rekindled their romance, which has left Rihanna's friend and mentor Jay-Z "deeply disgusted".

A source close to the situation told RadarOnline.com: "Jay was absolutely disgusted by what Chris did to Rihanna. Jay doesn't understand how a man could ever lay hands on a woman; it just goes against who he is and about. Chris is absolutely dead to Jay, he wants nothing to do with him ever.

"Now that Rihanna is hooking up with Chris and recording songs with him, Jay is deeply disappointed in her actions. He can't fathom why Rihanna is doing the things she is doing."

Jay is said to be "adamant" Rihanna should never forget what Chris - who is thought to be dating model Karrueche Tran - did to her when they were together, while the '99 Problems' rapper is concerned about what her fans will think about the pair's secret rendezvous.

The source added: "He understands the need for forgiveness, but he is adamant that Rihanna shouldn't forget what Chris did to her.

"Jay wonders what kind of message this is sending to Rihanna's young female fans. Rihanna knows how Jay feels about Chris, but she doesn't care, she is going to do what she wants."

The 42-year-old rapper - whose wife Beyonce Knowles gave birth to their first child, daughter Blue Ivy, last month - is said to have warned Rihanna that meeting up with Chris again "isn't going to end well".

The insider added: "He is even more protective of the women in his life. Jay has told Rihanna he will never give his blessing for what she is doing with Chris. He has told her, this isn't going to end well, it never does. In Jay's opinion, Chris has rage issues that he doesn't think have been dealt with."