Prince Harry's inheritance payday on 40th birthday to eclipse Prince William's cut as 'the spare': expert

Prince Harry is expected to have a very happy birthday this year.

On the Duke of Sussex’s 40th birthday – Sept. 15 – the British royal is expected to get a significant cash haul due to arrangements made by his late great-grandmother.

The Queen Mother died in 2002 at the age of 101.

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"The Queen Mother placed two-thirds of her [estimated] $120 million fortune into a trust fund for her great-grandchildren," Christopher Andersen, author of "The King," explained to Fox News Digital.

"She knew that when Prince William became Prince of Wales, which he did when his father became king, he would inherit the Duchy of Cornwall, which now boasts assets of over $1 billion," he shared. "In divvying things up, the Queen Mother may have left Harry a skosh more. In the meantime, the value of the trust has simply increased, Harry's share along with it."

The U.K.’s Mirror reported Harry will receive $8.5 million from his share, which is more than William received.

"Prince Harry is set to receive more money than Prince William because he is the spare," Kinsey Schofield, host of the "To Di For Daily" podcast, claimed to Fox News Digital. "The Queen Mother knew he would have fewer opportunities and responsibilities. It was a logical and thoughtful decision.

"There will be no tensions as [the family] knew about this arrangement for decades. Prince William likely quietly inherited his share two summers ago when he turned 40."

Andersen said there’s a good reason the trust doesn’t kick in until the big 4-0.

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"Prince Harry is set to receive more money than Prince William because he is the spare."

— Kinsey Schofield, host of the "To Di For Daily" podcast

"Why 40? To a woman who nearly lived to be 102, one can only imagine that 40 seemed like the perfect age to come into some extra cash — when you're young enough to appreciate it but also old enough, and hopefully wise enough, not to blow it," said Andersen.

"Of course, the princes' great granny couldn't have anticipated all the trouble Harry caused the rest of the family. I think she would have cut him out of [the trust] entirely had she known."

The U.K. Times reported in 2020 that Harry received a bequest from the Queen Mother, who put the bulk of her wealth into a trust fund for her grandchildren.

The outlet reported in 2002 that Queen Elizabeth II had avoided paying an inheritance tax of almost £20 million (about $25 million) on her mother’s legacy. This move enhanced the value of her grandchildren's fortune. It also revealed that both William and Harry paid £8.4 million (about $10 million) in inheritance taxes on the £21 million (about $27 million) estate of their late mother, Princess Diana.

Harry, 39, is required to pay taxes on any of his future commercial earnings, the outlet added.

While Harry will get a bigger payout than his brother on his birthday, William’s pockets aren’t empty.

On Thursday, the Duchy of Cornwall published its Integrated Annual Report for the 2023-2024 financial year, which marks William’s first full year as the Duke of Cornwall. The heir to the British throne inherited the estate and title from his father, King Charles III. The inheritance was passed on to William when Charles, 75, ascended to the throne.

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Queen Elizabeth, England’s longest-reigning monarch, died in 2022. She was 96.

William, 42, received just over $30 million from his first full year's income from the Duchy of Cornwall estate.

As a working member of the royal family, William doesn't receive a traditional income, People magazine reported. According to the outlet, his annual expenses are largely covered by the Duchy of Cornwall, which was established by King Edward III in 1337 to provide funds for the heir.

The outlet reported that the estate, worth over $1 billion, spans 130,000 acres across 23 counties in England and Wales. It includes land, farms, houses and other assets to support the heir and the heir's family. It is understood that William pays income tax on the entire income he receives after subtracting household expenses. Those have not been specified.

"It seems Prince Harry has drawn the lucky straw when it comes to the trust," British broadcaster and photographer Helena Chard told Fox News Digital. "The difference in the allocation of monies is attributed to what is thought to be Prince William and Prince Harry’s future financial prospects.

"Prince William has the Duchy of Cornwall, a private estate that he benefits from. Prince Harry will never privately benefit from this," Chard noted. "The late Queen Mother didn’t want her great-grandchildren to access their inheritance whenever and spend it willy-nilly. She placed the money in a trust fund in 1994 and stipulated that the recipients should reach a certain age before inheriting the money.

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"I’m pretty sure that the late Queen Mother never dreamed that Prince Harry would stand down from full-time royal duties," Chard continued. "She would have assumed that he would always have been Prince William’s right-hand man. I imagine there are a lot of mixed feelings regarding the inheritance split. Ultimately, the royal family will be relieved that Prince Harry has sufficient money to keep him out of mischief."

While William was destined from birth to be king, Harry, who is fifth in line to the throne behind his brother and William’s three children, has often appeared to struggle with the more ambiguous role of "spare."

He chose "Spare" as the title of his 2023 memoir, which recounted a lifetime of sibling grievances, from William getting the bigger bedroom at Balmoral Castle to a ferocious argument in which Harry claims William ripped his necklace and knocked him down onto a dog bowl.

"The Queen Mother always favored Prince William," said Schofield. "She spent a significant amount of time with him when he was a child. She would call William over to spend time with her and leave Prince Harry in a corner with the nanny. It was clear favoritism that drove Princess Diana crazy.

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"The Queen Mother had an enormous influence on King Charles's life as a very young boy and helped mentor him in his role as a future sovereign," Schofield added. "After spending so much time shaping the former Prince Charles, the Queen Mother wanted to have a similar relationship with Prince William. She taught him about his elders and expectations."

In "Spare," Harry alleged the British media treated him and his wife Meghan Markle as villains compared to virtuous William and his wife Kate Middleton. Harry also accused palace officials of lying to protect his older brother.

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The Sussexes cited the media’s racist treatment of Meghan, who is biracial, and a lack of support from the palace as reasons for their decision in 2020 to quit royal duties and move to the U.S.

In an explosive interview with Oprah Winfrey in 2021, the couple portrayed the royal family as indifferent to Meghan’s mental health struggles and suggested an unnamed family member had made a racist comment to Harry before the birth of their son, Archie. Harry described his relationship with William as "space at the moment."

Harry lives in California with his wife and their two young children.

The Associated Press contributed to this report.