Usher was left blind-sided in an Atlanta, Georgia courtroom on Wednesday when his ex-wife's lawyer accused him of sleeping with another woman during a cross-examination about the reinstatement of a nanny.
The singer was on the attack over his former wife Tameka Foster's decision to hire a babysitter, who had left the couple's employ during their marriage, without his knowledge when the attorney suggested he had a hidden motive to keep the woman away from his kids.
She suggested the nanny had "travelled to Miami (Florida)" with Usher and he had left after he was "discovered in bed with Maya Fox Davis?"
Usher's lawyer immediately objected, insisting the line of questioning was "absolutely irrelevant".
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The star seemed shocked and puzzled by the sudden sex talk.
Shortly after the courtroom showdown, the custody battle between the bitter pair went into recess. Usher and his ex will return to court in July.
During the three-day stand-off in the Fulton County courtroom, Usher, who is fighting for more visitation, accused his ex of spitting on his girlfriend and throwing a plate of food at his car in a jealous rage and he also appeared to tear up when he was quizzed about his capabilities as a dad and drug use.
Foster and Usher divorced in 2009 after two years of marriage. They have two young sons.