The Duchess of York made a surprising revelation during an Australian radio interview when she discussed her close relationship with her ex-husband Prince Andrew while visiting the country.

The 57-year-old, popularly known as Fergie, openly spoke about the Duke of York – who she divorced 20 years ago – to hosts Kyle Sandilands and Jackie O Henderson on the top-rated Kyle and Jackie O Show in Sydney.

On responding to whether she would ever reunite with her former husband, with whom she has two daughters, Princess Beatrice and Princess Eugenie, she divulged: "I always think, 'have we really? We're divorced to each other right now. We've never really left each other."

Sandilands suggested: "You're still together, sort of?" before Ferguson bluntly replied with, "Yes."

"I think the happily ever after...I'm actually writing a book about that, too," she added.

Friends of the former couple have claimed that Ferguson and Prince Andrew do not feel able to remarry while Prince Philip is alive because of his strong disapproval of the Duchess. During the Royal Ascot of 2015, when Andrew brought along his ex-wife as his guest, Prince Philip was reportedly heard to mutter: "What is that ghastly woman doing here?"

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Prince Andrew with his daughters Eugenie and Beatrice and his brother Prince Edward Peter Nicholls/Reuters

Ferguson and Prince Andrew separated in 1992 and divorced in 1996. She lived in Andrew's home at Royal Lodge for many years and now shares ownership with him of a £13 million ski chalet in Switzerland.

The mother-of-two gets on better with the Queen than her former father-in-law, but admitted on the KIIS 106.5 show that she is still terrified of her.

When O Henderson asked, "Who was the last person you got tongue-tied over?" Ferguson replied: "I always get really nervous before meeting the boss," explaining she meant the Queen.

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Princess Beatrice, Sarah Ferguson and Prince Andrew Getty

"But does she make you feel at ease and comfortable in her presence? Oh, of course, she's brilliant. She makes you feel comfortable within the first five seconds."

Ferguson's comments came as Prince Andrew made headlines yesterday over his reported dispute with his elder brother, Prince Charles, over the roles of his daughters as potential taxpayer-funded royals. Charles is said to have resisted the idea, while the Queen is at the centre of the row. Read the full report here.

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Queen Elizabeth II and the Duke of Edinburgh arrive for a reception and awards ceremony at the Royal Academy of Arts, Burlington House, London Jeff Spicer/ PA