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She has long been known as the 'hardest working royal' - and now, experts say it may well have earned her a small fortune.

As the King's sister, Princess Anne is devoted to The Firm and has even this week delayed the start of her annual summer break, instead stepping out for an engagement in Edinburgh on Monday.

Set to turn 76 next Saturday, the late Queen Elizabeth's only daughter, after 57 years of service, could be worth between £15 and £20 million, a royal author has claimed.

Speaking to the Daily Mail, writer Norman Baker explained that she is not only dedicated to her duties - but is also notoriously frugal.

'Notwithstanding her advanced years, she regularly tops the poll as the royal who carries out the most public engagements, putting younger royals like Prince William to shame,' he said.

'This year alone, she has visited South Korea and Thailand to strengthen diplomatic ties, attended the Commonwealth Games in Edinburgh, and undertaken trips to destinations as varied as Milan, Northern Ireland, and Jersey.

'In 2025, she notched up 478 engagements, and over her lifetime has passed the 11,000 mark. She believes in duty, and quietly gets on with her work, showing no signs of stopping.

'She has also over the years quietly put together a small fortune, and is thought today to be worth between £15 and £20 million.

'It helps that she is notoriously frugal. A satirical piece in Private Eye in 2021 has her giving gems of advice such as "a piece of Ryvita makes a perfectly acceptable starter. If you prefer something more fancy, you’re welcome to a bit of marge".'

Set to turn 76 next Saturday, the late Queen Elizabeth's only daughter, after 57 years of service, could be worth between £15 and £20 million, a royal author has claimed. Pictured at Ascot in 1980

Princess Anne at the 2018 Commonwealth Games, sporting an ensemble she has had for decades

Norman, who penned And What Do You Do? What The Royal Family Don't Want You to Know, the hard-hitting 2019 analysis of royal finances, said that Anne's wealth is made up of four main elements.

'First and foremost is her house, Gatcombe Park, given to her and her then husband Mark Phillips by the late Queen in 1976,' he explained.

'This Grade II listed building dates from the 1770s, and is actually only six miles from Charles’s beloved Highgrove House.

'The house boasts nine bedrooms, four reception rooms, a library, a billiard room, and a conservatory. It is thought to be worth upwards of £6 million today, though any house with a royal connection can expect to add a premium to the selling price.

'Besides the house, Anne has amassed over the years an impressive and expensive collection of jewellery, as indeed all female royals do. The collection, which includes a pearl necklace worth £1 million and a dazzling collection of tiaras, is estimated to be worth a further £5 million in total.

'Thirdly, she has her inherited wealth, benefiting from trusts established for her, most notably by the late Queen Mother. The royals take great care to ensure wealth is passed down the generations with the minimum possible amount of tax paid.

Norman, who penned And What Do You Do? What The Royal Family Don't Want You to Know, the hard-hitting 2019 analysis of royal finances, said that Anne's wealth is made up of four main elements. Pictured in 1984

Anne - known for her fondness of rewearing clothes - wearing an 80s ensemble in the 2000s

'Lastly, she receives from Charles, and before him his mother, a generous allowance to reflect the work she does. By the turn of the century, this was already £225,000 a year, and of course the cost of expenses such as travel are met on top of this.'

It comes as Anne earlier this week attended a rehearsal for the Royal Edinburgh Military Tattoo, which began on Friday.

Dressed in a traditional tartan skirt and cream jacket, Anne met with Robert Aldridge, the Lord Provost of the City of Edinburgh, alongside military personnel taking part in this year's demonstrations.

Pictured clutching a bouquet of blue, white and purple flowers, Anne was all smiles as she spoke with members of the Vancouver Police Pipe Band, who are set to perform at the annual performance at the Scottish Capital's historic Castle.

The princess also took time to meet with the Royal Regiment of Scotland and the Royal Air Force before observing a rehearsal in anticipation for the main event.

The visit took place as other members of the Royal Family have already began their traditional summer break - with King Charles and Queen Camilla retreating to Scotland to take time away from their engagements.

The Princess Royal has often expressed an interest in the Royal Edinburgh Military Tattoo, which first took place in 1950 on the esplanade of the city's Castle.

According to the organisers of the prestigious event, Anne regularly attends rehearsals held at Redford Barracks 'to meet members and those working behind the scenes' in the run-up to the annual Edinburgh Fringe Festival.

This year's Tattoo, which is part of the wider Edinburgh Festivals programme in August, is themed 'A Call to Gather' and will run from August 7 to August 29.

Anne has always held a particular regard for Scotland, having served as president of the Scottish Rugby Union for more than 40 years.

She is a Knight of the Thistle, Chancellor of the University of Edinburgh, and has twice served as Lord High Commissioner to the General Assembly of the Church of Scotland.

Her innumerable patronages, this side of the Tweed, include the Royal Edinburgh Military Tattoo and the Royal (Dick) School of Veterinary Studies.