US lawyer Alan Dershowitz, accused of having sex with an under-age girl in a case also involving Prince Andrew, has begun legal action to clear his name.
The Duke of York and Mr Dershowitz were named in US court papers relating to the handling of a case against financier Jeffrey Epstein.
Lawyers representing the complainant, now an adult, say they are preparing to present evidence of her claim.
Buckingham Palace says the sex claims against the duke lack "any foundation".
Mr Dershowitz filed papers at a court in Florida, where the case is being heard, to contest what he described as "absolutely outrageous claims".
The former Harvard law professor has asked for his name to be removed from documents which accuse him and Prince Andrew of having sexual relations with Virginia Roberts, known in court as Jane Doe #3, who was under the age of consent at the time of the alleged incidents.
In his submission to the court, Mr Dershowitz said he had been a victim of "salacious and scurrilous" allegations and wanted to take action to protect his reputation.
Before his papers were filed, lawyers for the woman said they stood by their story and challenged Mr Dershowitz to provide any evidence that he believed would refute their allegations.
The lawyers later filed a lawsuit against Mr Dershowitz, claiming comments he made during media interviews amounted to defamation against them.
Speaking to Reuters news agency about his legal action, Mr Dershowitz said: "We file a sworn declaration categorically denying the charges and proving by records and other travel documents that I could not have been in the places that she says that she had sex with me.
"We file a motion to intervene in the court and then we file a defamation action against the two lawyers and the woman. And then we file disbarment proceedings against the two lawyers."
Ms Roberts and another woman are attempting to bring their case to court by joining action already being taken by two other women, part of a wider case involving Epstein.
Ms Roberts's lawyers issued a statement following Mr Dershowitz's declaration being filed, stating that the four women "do not oppose Mr Dershowitz having an opportunity to present his arguments to the court.
"Jane Doe #3, however, has been viciously attacked by Mr Dershowitz.
"We have requested an opportunity to meet with the US Attorney's Office for the Southern District of Florida so that we can seek their assistance in presenting evidence (including evidence possessed by the government) that will help Jane Doe #3 respond to these unfair attacks."
BBC royal correspondent Peter Hunt said Mr Dershowitz's submission questions the woman's credibility, and that would not harm Prince Andrew.
However, there was little prospect of Prince Andrew following suit and providing a sworn statement of denial, he added.
BBC legal correspondent Clive Coleman said there was no constitutional bar on the prince suing and it would not be unprecedented as other members of the Royal family had done so, but generally not for libel.
The claims made against Mr Dershowitz and the prince were part of evidence submitted to a court in the US.
Two women, whose names have not been revealed but are referred to as Jane Doe #1 and Jane Doe #2, are suing the US government. They claim that it failed to protect their rights when it entered a plea deal with Epstein - who spent time in jail in 2008-9 for a sex offence with a minor.
Two more - Virginia Roberts and a woman known as Jane Doe #4 - now want to join the case.
Documents filed in a Florida court last week allege that Ms Roberts was sexually trafficked by Epstein, who forced her to make herself available for sex to "politically connected and financially powerful people".
Ms Roberts claims she was forced to have sex with the prince on three occasions - in London, New York and on a private Caribbean island owned by Epstein - between 1999 and 2002, when she was under age according to US law.
Epstein and Prince Andrew were formerly friends and the pair were photographed meeting in December 2010, after the tycoon had served his prison sentence.
The prince later had to apologise for his friendship and stepped down as the UK's special representative for trade and investment.
It is understood Prince Andrew, who is fifth in line to the throne, is now back in the UK after a skiing holiday in Switzerland.
It is likely the 54-year-old's first public appearance will be at a reception at the World Economic Forum in Switzerland later this month.
A royal aide has said the prince will "move on and push ahead" with his work, describing him as "resilient".
The prince's former wife, Sarah Duchess of York, who had gone on the skiing holiday with him, has spoken out in his defence.
"He is the greatest man there is. It was the finest moment of my life in 1986 when I married him," she told reporters. "He is a great man, the best man in the world."
London Mayor Boris Johnson said he had sympathy for the prince, when asked a question about him on his monthly LBC radio phone-in show.
"Prince Andrew does a huge amount of unsung and unheralded work for this country," he said.
"People go on and on about air miles but I have seen that guy get out there and sell this country, trying to help British firms to get business around the world."