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