A royal author has claimed that Prince Harry could have lost his huge inheritance had his relative known what was to come in his relationship with the Royal Family.

The Duke of Sussex is set to receive a financial boost of £7m in just a few short weeks when he turns 40. The windfall will come from money left to him by his great grandmother the Queen Mother who placed her immense fortune into a trust for her family.

Speaking to Fox News about Harry’s upcoming inheritance, Christopher Andersen explained why the former second in line to the throne has had to wait so long for the cash. He also ruminated on whether he would have received it had the Queen Mother known the future.

He explained: “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.

“Of course, the prince’s 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.”

Since the death of the Queen Mother in 2002 – when Prince Harry was 18 – a lot has changed with the prince and wife Meghan Markle stepping down as senior royals.

A feud has also developed between Harry and his brother Prince William over comments made by the Sussexes in a series of interviews and publications.

According to Mr Andersen, despite William’s position as heir to the throne, he received less than his younger brother when he turned 40 two years ago because he was not the ‘Spare’.

He explained: “The Queen Mother knew he would have fewer opportunities and responsibilities. It was a logical and thoughtful decision.”

Despite their increase in wealth Harry and Meghan’s combined wealth – said to be around £11million – will still be far below that of other royal couples such as William and Princess Kate.

The Prince and Princess of Wales are worth close to £1bn (£960m), nearly ten times that of Harry and Meghan who have been trying to build their income through opportunities in the USA.

Earlier this year it was claimed by one royal commentator that Meghan believed life in the Royal Family would be “filled with endless deference and untold wealth”.

Speaking after the launch of Meghan’s latest lifestyle project American Riviera Orchard, Tom Quinn argued she “abandoned” her successful blog The Tig because of the potential riches that awaited her.

Speaking to the Mirror, Mr Quinn said: “Meghan's new brand, American Riviera Orchard, has already gained popularity with over half a million followers, but it's essentially just a rebranding of The Tig.

"The brand she abandoned when she married Harry, thinking that life as a royal princess would be filled with endless deference and untold wealth.

“We don't yet know exactly what the new brand will be selling, but it's astonishing that a Royal prince and his wife have been reduced to selling some of the things we have already been told they will be selling - marmalade, jams and even dog shampoo.”