Sarah Margaret Ferguson was born on 15 October 1959 at Welbeck Street in London and grew up at Dummer Down Farm in Hampshire, the second daughter of Major Ronald Ferguson, who managed Prince Philip’s polo, and Susan Barrantes.

She was educated at Hurst Lodge in Berkshire and left at sixteen for a secretarial course, then worked in a London art gallery and in public relations. She married Prince Andrew in July 1986 and became Duchess of York, a title she has kept since the couple separated.

Her working life before the marriage was ordinary and salaried: gallery assistant, then a job with a small publishing and public relations firm. It gave her a publishing contact book that later mattered more than the salary did.

She began writing while still a working member of the royal family. Two illustrated histories of the royal art collections appeared in the late 1980s, and in 1989 she created Budgie the Little Helicopter, a children’s series that ran to several titles and was adapted into an animated television programme in the mid-1990s.

The 1996 divorce is where her finances start properly. The New Zealand Herald, reporting figures given by the Sunday Telegraph, put the overall settlement at about £3 million: £500,000 for her to buy a house, a £350,000 cash payment, £500,000 towards school fees and a £1.4 million trust for Princesses Beatrice and Eugenie. The trust was the daughters’ money; roughly £850,000 was hers.

The writing paid considerably better. The same reporting put her earnings from the autobiography My Story, published that year, at £2.2 million — about two and a half times the cash she took from the divorce, and by some distance the biggest payment her own work has produced. It is the figure to hold on to: her wealth has come from the page and the screen, not from the Crown.

Adding the rest of the output, our estimate is £6 million to £10 million gross from roughly fifty further titles over thirty-six years — children’s books, diet and cookery titles, later memoirs and two historical novels — plus £3 million to £6 million from television and speaking.

Budgie the Little Helicopter is the commercial high point of her authorship: a series that sold internationally, carried merchandising and reached television. Mills & Boon published her first adult novel, Her Heart for a Compass, in 2021, written with the historical novelist Marguerite Kaye and based on her own great-great-aunt; it became a Sunday Times bestseller and was followed by A Most Intriguing Lady in 2023.

On screen she has fronted documentaries, appeared as a regular guest on American and Italian television and, since 2021, presented a podcast. In 1993 she founded the charity Children in Crisis, which worked in education in west Africa and central Asia for more than twenty-five years.

She has been one of the most photographed women in Britain since 1986, and the interest has never much depended on what she was doing. Her weight, her finances and her friendships have all been tabloid subjects for four decades.

Her rehabilitation as a public figure has run mostly through publishing and broadcasting. The book-club and podcast work of the 2020s gave her a following of her own, largely among readers of historical romance, and reviewers of the novels treated them as genre fiction rather than curiosities.

The Weight Watchers contract was the most valuable commercial deal of her life. Deseret News reported in January 1997 that she would take about $1 million a year as the company’s American spokeswoman, at a point when she was carrying multimillion-dollar debts.

She held the role for roughly a decade, which on our working returned something in the order of $8 million to $10 million gross, or £5 million to £6 million. Other endorsements have been smaller and shorter: skincare, tea, jewellery and furnishing ranges, and paid appearances.

Her ventures have been the least successful part of her financial life. Hartmoor LLC, an American lifestyle and wellness company she launched in 2008, collapsed the following year; ABC News reported it owed creditors more than $1 million, who were expected to recover between 50 and 75 cents in the dollar.

Earlier and later efforts followed a similar shape: a production company, a licensing arrangement for her children’s characters, and a series of promotional partnerships. The pattern is a large personal brand attached to small undercapitalised companies, which is why we value almost none of it in the estimate below.

The house she has lived in for most of the past two decades is not hers. Royal Lodge in Windsor Great Park is Crown Estate land held on a lease taken by Prince Andrew, and no part of its value belongs to her. The same is true of anything held by the royal family or the Crown.

Her one substantial property asset was a half share in Chalet Helora in Verbier, bought jointly with Andrew in 2014. International Business Times reported it on the market at £18.6 million, and it sold in 2022 for a figure reported at about £19 million after a £6.7 million claim by the previous owner was settled.