Virginia Giuffre's family have said the police probe into the sex offence allegations facing Andrew Mountbatten-Windsor is 'huge' and gives them 'hope' after she 'paved the way' for an investigation.
Police revealed on Friday that they are investigating a claim by a non-British woman who says she was flown to the UK by Jeffrey Epstein for sex with the former prince.
The unnamed trafficking victim alleged she was in her 20s when, at the paedophile's request, she spent a night with Andrew at his Royal Lodge home in Windsor.
The woman claims she had a sexual encounter with him and was then taken to Buckingham Palace for tea afterwards in 2010. She was also apparently given an exclusive tour.
She is the only Epstein accuser who says she slept with Andrew at a royal residence.
Thames Valley Police has spoken to her lawyer but officers are yet to carry out interviews because she has not made a formal complaint.
Specialist detectives have told her attorney, the same man who represented Ms Giuffre, that they will speak to her only when, and if, she feels ready.
Now Ms Giuffre's family have said the police probe gives them 'hope' after she 'paved the way' for an investigation.
Officers are assessing separate claims that Jeffrey Epstein sent a woman to the UK for sex with Andrew in 2010, mirroring accusations made by the late Virginia Giuffre
Andrew Mountbatten-Windsor, pictured leaving Aylsham Police Station in February, is being investigated by the police over potential sexual offences
Speaking to Sky News on Friday, Ms Giuffre's sister-in-law, Amanda Roberts, said: 'I think initially it's very encouraging.
'You know, initially it was only we were hearing that it was going to be investigations of conduct, like sharing government information.
'And to hear that the potential of investigating sexual crimes, that is huge. It is more than what we are seeing here in this country and it actually gives us hope.
'And Virginia paved the way for that. If it wasn't for her courage and her bravery and being persistent in her truth, you know, we wouldn't be here and we are so thankful for the police to really be taking this seriously.
'And it was good news for us today so I think we're very hopeful.'
Andrew remains under investigation and has always strongly denied any wrongdoing.
Thames Valley Police announced on Friday morning that they are investigating the former prince over potential sex offences.
In a bombshell development, detectives announced that a misconduct in public office probe into Andrew has broadened to consider a wide range of offences, including sexual misconduct and corruption.
The former prince is seen crouching over an unidentified woman in one of the photos released in the Epstein files
Virginia Giuffre's family has said she 'paved the way' for the police investigation
Three months after the former Duke of York was arrested over claims that he leaked secrets to paedophile financier Jeffrey Epstein during his decade as the UK's trade envoy, officers are now interviewing witnesses about suspected criminal offences.
Thames Valley Police will today make a public appeal for potential 'victim survivors' to come forward.
It comes after the force identified 'multiple lines of inquiry' in what is being described as a 'significant investigation'.
Police have seized evidence in a raid of Andrew's former home at Royal Lodge, Windsor, and his new property on the Sandringham Estate in Norfolk, which officers are now said to be 'carefully working through', it is understood.
The major update follows the release of new documents on Thursday relating to Andrew's appointment as trade envoy.
They revealed that the late Queen was 'very keen' for her son to take on a 'prominent role in the promotion of national interests' when her cousin, the Duke of Kent, stepped down from the role.
Andrew had a preference for missions to 'sophisticated countries' but should not be 'burdened' with the meetings and paperwork associated with the role, the files released by the Government showed.
The 15-page document was published following pressure from MPs in the wake of the Epstein files being made public by the US Department of Justice.
They suggested the then-duke was sharing potentially commercially sensitive information, gleaned from his official post, with Epstein.
Police descended on his home at Wood Farm in February, taking Andrew into custody on his 66th birthday.
He was released some 11 hours later under investigation.
Thames Valley Police have now revealed that senior officers are already speaking to the Crown Prosecution Service for 'early investigative advice' ahead of a potential prosecution.
They are also liaising with the US Department of Justice to formally request evidence contained in the millions of documents from the Epstein files.
Alongside the allegations from the files, they are assessing separate claims that Epstein sent a woman to the UK for sex with Andrew in 2010, mirroring accusations made by the late Virginia Giuffre, who said she was trafficked to have sex with the former duke.
The mystery woman's attorney Brad Edwards, who represents more than 200 alleged Epstein victims, has said that Andrew and the Royal Family will have to sit down and discuss the claims soon or face court action.
Mr Edwards previously sued Andrew on behalf of Virginia Giuffre, who alleged she had sex with the former Duke of York in London, New York and on Epstein's Caribbean island.
Andrew settled a New York civil case brought by Ms Giuffre for a reported £12million without any admission of liability. He has vehemently denied her claims in the past.