Heather Mills, Sir Paul McCartney's ex wife, is to give evidence to the Leveson Inquiry into press standards on 9 February.
Mills is expected to answer questions relating to evidence from former News of the World editor Piers Morgan.
Chat show host Piers Morgan previously told the inquiry that he had listened to a voicemail message left to Mills by Sir Paul, but refused to say when or where he heard it because he wanted to protect a "source".
Mills subsequently issued a statement in which she denied disclosing private messages to Morgan.
She claimed he had used her as a "scapegoat", adding that she would be happy to answer questions from the inquiry.
Daily Mail editor Paul Dacre, who appeared on Monday, will return to the inquiry, having been recalled to submit further evidence about claims made by actor Hugh Grant.
The former assistant editor (news) of the News of the World, Ian Edmondson, will also give evidence.
He was arrested on suspicion of conspiring to intercept voicemail messages last year and is set to answer bail in March.
Other witnesses appearing at the Royal Courts of Justice in central London today include PR guru Max Clifford, Darryn Lyons, who founded picture agency Big Pictures, and general secretary of the National Union of Journalists, Michelle Stanistreet.
Prime Minister David Cameron set up the Leveson Inquiry last July in response to revelations that the News of the World commissioned a private detective to hack murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.
The first part of the inquiry, which is now coming to an end, is looking at the culture, practices and ethics of the Press in general and is due to produce a report by September.
The second part, examining the extent of unlawful activities by journalists, will not begin until detectives have completed their investigation into alleged phone-hacking and corrupt payments to police, and any prosecutions have been concluded.
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