Heather Mills is to give evidence at the Leveson Inquiry into press standards, it has emerged.
The ex-wife of Sir Paul McCartney is expected to answer questions relating to evidence from former News of the World editor Piers Morgan.
When giving evidence in December, Morgan told the inquiry he would not disclose a source who played him a tape of a message that Sir Paul left Mills.
He said: "I am not going to discuss where I heard it or who played it to me. I don't think it's right. In fact the inquiry has already stated to me you don't expect me to identify sources."
Lord Justice Leveson told Morgan the only person who would be able to lawfully listen to the message was Mills or somebody authorised on her behalf.
He told Morgan: "I am perfectly happy to call Lady McCartney to give evidence as to whether she authorised you to listen to her voicemails.
"She may say she did in which case you're not compromising anybody, but if she didn't then we can proceed on the premise that it's somebody else, can't we."
Ms Mills is expected to appear at the inquiry, sitting at the Royal Courts of Justice in London, on Thursday morning.
Also appearing is Paul Dacre, editor-in-chief of Associated Newspapers, which publishes the Daily Mail and The Mail on Sunday, who has been recalled to the inquiry.
He will answer more questions about accusations made by actor Hugh Grant.
