The pop star, who has dated some of Hollywood's most beautiful women, said his mum was furious when she discovered him with the unidentified lover.
'My mom was not cool about it. I was too young to be in bed with a girl, she was upset,' Timberlake said in August's edition of Elle magazine.
And Timberlake also said he is worried about the amount of skin he shows off in his latest movie Friends With Benefits.
'I will be honest and say that I'm still trying to get into the editing room to cut down on my ass time,' he said.
'I am like, 'Oh my God, my mom's gonna see that'.'