Andrew Mountbatten-Windsor allegedly invited a 20-year-old model to partake in unconventional sexual activities to fulfill his “wildest fantasies,” according to claims made by his royal biographer.

Revealed in a sensational book excerpt featured by the Mail, author Andrew Lownie recounts the model’s encounter with the former Duke of York, now 65, during a charity event in the late 1980s.

The woman alleged that Andrew, recently stripped of his princely title, had “no boundaries” and that they had been intimate twice, with him asserting he was in an open marriage.

Lownie penned the unauthorized biography, “Entitled: The Rise and Fall of the House of York,” which details the dramatic decline of Andrew’s standing.

Within the book, the model is quoted as saying, “He wanted me to engage in kinky sexual activity. He had no boundaries.”

‘He told me he had an open marriage arrangement with his wife. After returning to London, I never heard from him again. 

‘I felt like he used me for a few days, so he could live his wildest fantasies.’

Moreover Andrew, who was nicknamed ‘Randy Andy’ at school and is believed to have slept with 1,000 women, was rumoured to have had an affair with a household staff member.

Andrew, the former Duke of York, is seen driving out of his home at Royal Lodge in Windsor

Andrew, Virginia Giuffre and sex trafficker Ghislaine Maxwell in a photo reportedly taken in 2001, when Giuffre was 17 years old

One nanny said she left because he made unwelcome advances and that employees were advised to steer clear of him. 

‘When I started, I was warned to stay away from him. He would sometimes enter the staff quarters,’ she said. 

‘It seemed everyone was aware of his behaviour, but little was done about it.’ 

The employee added: ‘Staff gossiped all the time, but a tape device was found in a flowerpot in the staff area, so it was difficult to speak after that.’

And according to Emma Gruenbaum, a masseuse at the Wentworth Golf Club that Andrew frequented, he often booked her for massages at Royal Lodge.

She said Andrew insisted on being naked and, and despite her objections, he would try to hug her and ask about her sex life. 

On one occasion, while she adjusted the massage table, he remarked, ‘Hey, nice ar**e. Do you take it up the a**e?’

She remembered how ‘all the way through he was talking about anal sex and making anal sex jokes. He asked when I had last had sex. It went on and on.

‘That’s just not normal behaviour for a professional sports therapy session. He was a constant sex pest from the start.’

King Charles is seen at Sandringham in Norfolk on Saturday afternoon

Emma Gruenbaum, a masseuse at the Wentworth Golf Club that Andrew frequented, claimed he often booked her for massages at Royal Lodge

Andrew was photographed on a luxury yacht off the coast of Sardinia with 25-year-old Spanish-Filipina model Alexandra Escat in 2010

It comes after Lownie claimed yesterday that during one taxpayer-funded trip to Thailand, the disgraced former prince had 40 prostitutes brought to his five-star hotel over just four days.

Lownie said on a Mail podcast: ‘In 2001, Andrew is 41, he’s having his midlife crisis and he basically starts chasing lots and lots of women.

‘He uses the excuse of his role as Trade Envoy, paid for by the taxpayer, to go off on these trips.

‘He always puts in two weeks of “private time”. So, we pay for his holiday and then he goes off and does things.

‘There was a famous trip to Thailand – for the birthday celebrations of the King. Andrew is representing his country and insists on staying in a five-star hotel rather than the embassy, which he always did.

‘Andrew had 40 prostitutes brought in the space of four days. This was all enabled by diplomats and others.’ 

On Thursday, Buckingham Palace announced King Charles had initiated a formal process to strip Andrew of his Prince title and served formal notice for him to vacate Royal Lodge.

They said in a cold statement: ‘His Majesty has today initiated a formal process to remove the Style, Titles and Honours of Prince Andrew.

Prince Andrew represented the British monarch at the King of Thailand’s diamond jubilee celebrations in 2006

An aerial view of Andrew’s current home – Royal Lodge in Windsor 

‘Prince Andrew will now be known as Andrew Mountbatten Windsor. His lease on Royal Lodge has, to date, provided him with legal protection to continue in residence.

‘Formal notice has now been served to surrender the lease and he will move to alternative private accommodation.

‘These censures are deemed necessary, notwithstanding the fact that he continues to deny the allegations against him.

‘Their Majesties wish to make clear that their thoughts and utmost sympathies have been, and will remain with, the victims and survivors of any and all forms of abuse.’

Andrew is understood to be ‘sanguine’ about the dramatic change in his circumstances which comes as a result of the recent revelations against him.

These include that Andrew told his friend, the paedophile Jeffrey Epstein, that ‘we are in this together’ – as was exclusively revealed by the Mail.

The family of Virginia Giuffre – who claimed to have been trafficked to and made to have sex with Andrew at 17 – are now also calling for him to face justice in the US.

Princesses Beatrice, 37, and Eugenie, 35, will retain their Royal titles despite their father no longer being a prince.

Angela Levin, a royal commentator and biographer, told the Daily Mail the pair will want to avoid him as much as possible but might have to ‘step up’ and parent their father if he becomes ‘desperate’.

She said: ‘I think Andrew will feel so crumbled about what has happened. He’s always been so pompous and trusting himself as being so clever.

‘For him to have everything taken away, and for that to happen in front of your children, who are grown up and can understand what he is being accused of, is very embarrassing to him, and for his own children. He will have to lean on them if he has no one else.’