Sarah Ferguson 'branded the single greatest threat to the monarchy by top aide'

Sarah Ferguson has been struck off by a slew of charities after an email that she wrote to convicted sex offender Jeffrey Epstein came to light. The ex-wife of Prince Andrew has long defended the disgraced Duke over his own connection to the paedophile financier, but now her friendship with Epstein has been brought under the microscope.

Only weeks after publicly disowning Epstein in a 2011 interview, she wrote him a gushing email apologising for what she had said about him, and calling him a "supreme friend". A spokesperson for Sarah has claimed she had received threats from the disgraced financier after the public comments she made about him, and, "this email was sent in the context of advice the duchess was given to try to assuage Epstein and his threats."

But while her immediate world is crumbling around her in the wake of the scandal, palace aides allegedly lived in fear that she would one day irreversibly damage the Firm's reputation, with one aide even going so far as to call her its "greatest threat".

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The claim was made when Sarah pulled out of a promotional tour to promote her children's book Budgie, the Little Helicopter, in 1989, according to John Sargent, the former head of Simon & Schuster's children's book division.

The publishers needed her to travel to New York, but Fergie apparently said the palace had blocked her. Sargent told the Telegraph that said he had to step in as the tour was a condition of her contract, and after a meeting with palace staff and the Duchess of York, eventually the royal household "relented, but it was tense".

Writing in his memoir, he later said that an aide had pulled him to one side to brief him on the background. "He apologised for being difficult. He understood it was about business for me. He explained that the Royal Family was different from anything I had ever experienced: 'Think of it this way, John. The Royal Family is like a Fortune 500 company, but in this case all of the management are relatives, and many of them are in-laws.

"And then he told me that the Duchess of York was the single greatest threat to the monarchy in the current era, and his job was to control that threat. He feared her lack of grace and popularity would stain them all."

The candid admission about Fergie's true status behind closed doors shocked the publisher, he claimed.

After the breakdown of Sarah and Andrew's marriage, which was filled with major scandals, it took many years for her to get back in the good books of her former in-laws.