His runaway nephew Harry got £15 million for writing his memoirs – so how much more can ex-Prince Andrew expect for his? That’s the thought racing through publishers’ minds this week as the disgraced former duke packs his bags and prepares to vacate Royal Lodge.

While speculation is rife that Sarah Ferguson is preparing to break ranks and write a tell-all book, publishers agree that the far greater prize would be Andrew’s tale – with his anecdotes of growing up in the world’s most exclusive family, then throwing it all away though his fatal association with Jeffrey Epstein.

And why not?

Back in the 1950s Andrew’s great-uncle, the Duke of Windsor, shocked his family and the wider royal court by announcing he was writing his life-story.

Then, hot on his heels, his wife Wallis announced she, too, would give her version of events which led up to the Abdication – the greatest crisis to hit Britain’s royal family in centuries.

In each case, they were motivated equally by money – and revenge.

The duke’s book, A King’s Story, was published in 1951, sending his brother King George VI into one of his famous ‘gnashes’, and making bitter enemies of previously loyal royal servants.

His former private secretary Sir Alan Lascelles seethed: “If you knew what that man had taken out of the country [when he abdicated], you would know that he does not need money. He is in a royal trade union, and the trade union rules are against this kind of thing, He is the meanest royal there has ever been.”

Writing about what had been, till then, a sacrosanct subject – the private life behind the royal public facade – was damaging to the Duke’s reputation and more important, the royal family’s, Lascelles said.

But Edward Windsor couldn’t care less. Wounded by never being allowed to return to the country he once ruled, and beside himself with rage that the Duchess was never to be allowed the title of Her Royal Highness, he knew he couldn’t be stopped from writing what he wanted.

Lascelles opined that the only way to stop him was to appeal to his better nature – “but I am sorry to say that long experience has convinced me he has no such feelings when the interests of the Monarchy conflict with his own.”

Fast-forward 70 years, and history is in danger of repeating itself. Unlike royal servants who are obliged to sign confidentiality agreements, Andrew Mountbatten-Windsor faces no such obstacle – he’s free to write what he likes.

If he likes. And all the indications are that he’s not taking his ousting from his family home of more than 20 years with good grace. Renowned for his arrogance and self-belief, it would not take much for a publisher to get him to spill the beans.

But how many beans? And how much would he get for spilling them?

“Obviously everyone wants the inside track on his time with Epstein,” a publishing executive told me. “That is the Holy Grail – no royal has been treated so brutally by his own people since King Charles I was beheaded in 1649, and he’s clearly angry at the way he’s been dumped. In those circumstances he might be prepared to talk, in broad terms, about his involvement with Epstein, simply to get his side of the story across.

“But he has to be careful his words don’t incriminate him. The Democrats in the US Congress have asked Andrew to appear before them, and now he no longer has royal immunity, he’d have to tread very, very carefully.

“But he must be dying to say something in order to salvage his professional reputation.”

Even if Andrew resists that temptation, there’s still a colossal amount he could tell. As Queen Elizabeth’s favourite son he would have plenty to say that we don’t yet know about our legendary monarch. And plenty more to say about his big brother Charles, who stripped him of his honours.

The price for even that – without the detail on Epstein – will far outweigh Prince Harry’s £15 million advance. One literary agent I spoke to this week told me: “We’re looking at maybe £25 million. With the right ghost-writer asking him the right questions, we could see the history of the House of Windsor completely rewritten with what he knows. He’s a time-bomb waiting to explode.”

So will Andrew do it?

Such a deal would almost certainly send him into exile – the Sandringham house arranged for him, and the various financial deals still being put into place, would have to go. He has inheritance money enough to keep him comfortable for the rest of his life, but to a man used to jet-setting around the world and rubbing shoulders with potentates, £25 million might sound like chicken-feed.

Not so Fergie, whose income bracket never came close to matching her ex-husband’s.

“But she’d have to do a deal with herself – to give up whatever housing arrangement the royals are working out for her, plus her income as mother of Queen Elizabeth’s grandchildren.” I was told. “In return – depending on how much she’s prepared to reveal – she could still match Prince Harry’s £15 million for her memoirs, maybe more.”

Back in the 1950s A King’s Story earned the Duke of Windsor the equivalent of £12 million in today’s money. The Duchess’s memoir The Heart Has Its Reasons – a quote from the 17th century philosopher Blaise Pascal, arguing for heart-over-head when it comes to making decisions - earned the equivalent of £6m. What with the settlement from Buckingham Palace they got when they left England for good, it was enough for the duke and duchess to get by on.

Andrew was never King, but what he knows – and what he’s prepared to tell – could well make the Abdication look like a teddy-bear’s picnic.

And Fergie, too, knows where the bodies are buried. Never will there have been a more stressful Christmas than the one ahead, as King Charles waits at Sandringham to discover the consequences of sending his brother and ex-sister in law out into the wilderness..