Actress Cameron Diaz is suing The Sun newspaper over a story claiming she was having an affair with a married man.
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The Hollywood star, who is in a relationship with singer Justin Timberlake, was pictured with another man on the front page on Thursday.
Her solicitors Schillings said the allegations were "false". The Sun was unavailable for comment.
The 32-year-old actress has enjoyed huge success in films including Charlie's Angels and Shrek.
"Cameron Diaz has today instructed her solicitors Schillings to issue and serve libel proceedings against the publishers of The Sun newspaper," a statement said.
The story was "falsely alleging that she had embarked upon a secret affair with a married man", it added.
Timberlake is taking unconnected legal action against the News of the World over a story that claimed he cheated on Diaz.
That case is expected to go to jury trial in London in October, Schillings partner Simon Smith said.