If the grapevine is to be believed, singer Beyonce Knowles is cheating on her husband and singer Jay-Z and she is reportedly having an affair with her bodyguard Julius De Boer.

Jay-Z, who got married to Knowles in 2008, is said to be suspicious about her close relationship with Boer, reports showbizspy.com.

`Jay definitely thinks that there was and may still be something romantic going on between Bey and Julius. He wanted to fire Julius last February, but Beyonce said- 'Julius isn't going anywhere'," said a source.

In 2009, Knowles, 32, and Boer were spotted leaving a hotel. Boer's lips were stained with the singer's signature red lipstick.

Despite being subject to numerous cheating rumours himself, Jay-Z is jealous of his wife's friendship with her bodyguard.

`They've spent a lot of time together behind closed doors. He's even stayed in her hotel room," added a source.