Prince Charles’ net worth is high enough to provide the long-time heir to the British throne with a kingly existence.

Estimates about how much money the heir apparently has in the bank tend to fall in the hundreds of millions. Go Banking Rates reported that he has US$100 million. Other estimates, however, are considerably higher. According to Time and Town & Country, he is worth around US$400 million. Regardless of how many millions of dollars is currently under the prince’s name, it is likely that not all of that money is constantly available to him.

Much of Prince Charles’ income derives from the Duchy of Cornwall. As the longest-serving Duke of Cornwall, he is entitled to the private estate’s annual revenue surplus.

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According to the duchy’s most recent financial statement, the revenue “does not cover official travel or property services, which are funded by the sovereign grant”. British taxpayers support the royal family through an annual sovereign grant.

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The mention of the British royal family’s riches might call to mind national treasures like the Crown Jewels or the Tower of London ... but Queen Elizabeth does not personally own those.

And neither will Prince Charles, once he inherits the throne. The Crown simply holds many priceless objects and historical structures in trust for Britain.

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The Crown’s Privy Purse – or private income – flows from the Duchy of Lancaster, a private estate that has been passed down from monarch to monarch since 1399.

But Queen Elizabeth’s eldest son does not rely on his mother for a pay cheque. As the Duke of Cornwall, he can take advantage of an entirely separate revenue stream.

The prince receives an annual income from the Duchy of Cornwall’s surplus revenues. The historic estate, which King Edward III launched in 1337, has traditionally been passed down to the eldest son of each reigning monarch.

Prince Charles became the heir to the throne when he was just three years old, but did not receive full access to the duchy until he turned 21 in 1969. That year, the prince’s income from the duchy was boosted to US$528,000 a year.

Prince Charles biographer Sally Bedell Smith wrote that the young prince opted to follow tradition and return around 20 per cent of his income to the government as a voluntary tax, meaning that he was left with a weekly income of around US$4,800.

She wrote that the Duchy of Cornwall provided Prince Charles with “independence from his parents and their court that he would use to the utmost in the years ahead” and permitted him to “underwrite his royal duties and help support his charitable enterprises”.

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What’s more, she wrote that his new-found riches enabled him to live a life of luxury “unequalled by his siblings” that ultimately “set him definitively apart from them”.

Charles has one younger sister, Anne, Princess Royal, and two younger brothers, Prince Andrew, Duke of York, and Prince Edward, Earl of Wessex. Expenses stemming from his younger siblings’ official royal duties are usually covered by the queen’s Duchy of Lancaster income.

Back when Prince Charles was 21, the duchy consisted of a huge swath of valuable farmland, Helford River oyster fisheries, granite quarries, London real estate, tin mines and even Dartmoor Prison, according to Smith.

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Today, the duchy owns 53,000 hectares of land across 23 counties of England and Wales, including Cornwall, Devon, Dorset, Herefordshire, Somerset, Gloucestershire, Kent and the Isles of Scilly.

The duchy’s latest report noted that its holdings included £58 million – or around US$74 million – worth of development sites, and £291 million – or US$374 million – worth of commercial property. According to the report, the duchy brought Prince Charles a £21.7 million – or over US$27 million – distributable surplus.

The duchy also comes with the perk of bona vacantia, meaning that the Duke of Cornwall’s estate has a right to the unclaimed property of deceased Cornwall residents who die without a will.

Elsewhere in Britain, such cases typically result in the property going to the British government. Between 2006 and 2012, £1 million – or US$1.2 million – worth of such property went to the duchy.

According to the Duchy of Cornwall’s official website, all funds obtained through bona vacantia went to the The Duke of Cornwall’s Benevolent Fund, which the prince established in 1975.

The duchy’s site reported that, since 2011, the fund has “donated over £850,000” – or US$1 million – to environmental, community, art, religious and educational organisations.

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The prince pays a voluntary income tax on his earnings ...

... but the duchy itself is not required to pay corporation and capital gains taxes. According to the Duchy of Cornwall’s website, however, “the Duchy's capital gains have to be reinvested in the business and cannot be distributed”.

Additionally, Prince Charles “has no access to the Duchy’s capital value”, according to the report. But the royal heir’s finances have not been without controversy. Like his mother, Prince Charles was caught up in the 2017 Paradise Papers leak, which shone a light on the offshore investments of the rich and powerful.

In 2007, the duchy secretly bought shares worth US$113,500 in the Bermuda-based Sustainable Forestry Management, which was then directed by the prince's friend and former Cambridge classmate Hugh van Cutsem.

Prince Charles – who has long supported environmentalist causes – went on to lobby for changes to climate change rules that would have benefited the Bermuda company, according to the International Consortium of Investigative Journalists. The duchy sold its share in the company for US$325,000 in 2008.

A duchy spokesperson told The Guardian that the estate’s accounts are “independently audited” and that “the Prince of Wales does not have any direct involvement in the investment decisions taken by the duchy. These are the responsibility of the duchy’s finance and audit committee”.

But the episode raised concerns about financial conflicts of interest. Sir Alistair Graham, the former chairman of the United Kingdom’s Committee on Standards in Public Life, told the BBC, “There’s a conflict of interest between his own investments of the Duchy of Cornwall and what he is trying to achieve publicly.”

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Beyond his connection with the Duchy of Cornwall, the Prince of Wales is also connected to a number of philanthropic efforts.

Founded in 1979, the Prince of Wales’ Charitable Foundation is both a grant-giving organisation and a project incubator, according to its official website. Time reported that Prince Charles has given US$72.5 million in grants over the years.

Part of Prince Charles’ Duchy of Cornwall revenue also goes to his immediate family. According to the duchy’s 2018 financial report, “The money is used to cover personal and professional expenditure – including staff, charitable work and public duties – for The Prince of Wales and The Duchess of Cornwall, The Duke and Duchess of Cambridge, and The Duke and Duchess of Sussex.”

The Prince of Wales has long advocated for environmental conservation, architectural preservation, and alternative medicine. He is also the patron or president of 400 organisations.

But Prince Charles’ wife Camilla, Duchess of Cornwall, likely came into the relationship with some money of her own.

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The duchess has a net worth of US$5 million, according to Good Housekeeping magazine.

One of the family’s biggest financial drains is reportedly travel expenses.

In 2017, the Prince of Wales’ trip to India, Malaysia, Brunei and Singapore cost about US$475,000, Town and Country magazine reported.

Once Prince Charles inherits the throne, he will begin drawing his money from the Duchy of Lancaster ...

... and Prince William will inherit the Duchy of Cornwall.

But, as of now, despite the fact that absolute primogeniture – the right of succession of a firstborn child – now determines who will succeed to the British throne, the Duchy of Cornwall can currently only pass to the eldest son of the reigning monarch.

The duchy’s website says: “When there is no male heir, the Duchy reverts to the Monarch, and the annual Sovereign Grant is reduced annually by the amount of the Duchy’s income.”

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This article originally appeared on Business Insider.