Prince Harry faces a monumental tax bill unless he takes a break from the Los Angeles mansion

Meghan, Duchess of Sussex and Prince Harry, Duke of Sussex, and their son Archie moved to Los Angeles after leaving a rented mansion in Canada. Photo / Getty Images

A "monumental" tax bill could be coming Prince Harry's way unless he takes a break from his £11 million Californian mansion next month.

Earlier this year he, Meghan and their son Archie moved to Los Angeles after leaving a rented mansion in Canada.

The family were first reported to be staying in a mansion owned by Tyler Perry located in Beverly Hills.

The pair and their son moved to LA earlier this year. Photo / Santa Barbaras Luxury Homes

As of October 4, the Prince has been in the US for 151 days and if he reaches 183 days he is legally liable to pay taxes in the country.

The Mail on Sunday reported a top LA lawyer David Holtz assumed Internal Revenue Service are watching him.

"You can safely assume that someone at the Internal Revenue Service [IRS] is looking very closely at him. This is a big deal."

The Mail on Sunday are reporting Prince Harry will face paying two sets of tax.

"Both US federal and Californian state taxes under the 'substantial presence test' that requires any foreigner who spends 183 days in the country during a three-year period to pay US taxes on worldwide earnings."

"Harry's bill could be monumental and could open up a can of worms for the Royal Family because the IRS will want to know all his sources of income" said a tax expert.

"That's not just his Netflix deal, but any monies he might have received in gifts from Prince Charles and any trust funds, savings accounts or other assets he has in the UK. That means the Royal books will be open to scrutiny. The US taxman is far more zealous than his UK counterpart."

The Duke and Duchess of Sussex are estimated to have a joint fortune of £20 million. Photo /Santa Barbaras Luxury Homes

It is thought the couple received $1 million for a speech at an event earlier in the year, alongside also signing a multi-year deal with Netflix.

The Mail on Sunday understands it is worth between $3-5 million a year.

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This afternoon, The Duke and Duchess of Sussex attended the annual Commonwealth Service at Westminster Abbey on Commonwealth Day, alongside Her Majesty The Queen and Members of The Royal Family. The Commonwealth is a global network of 54 countries, working in collaboration towards shared economic, environmental, social and democratic goals, and the Service today seeks to highlight the vast community which spans every geographical region, religion and culture, embracing diversity amongst its population of 2.4 billion people, of which 60 percent are under 30 years old. As President and Vice-President of the @Queens_Commonwealth_Trust, The Duke and Duchess of Sussex have been passionate advocates of the Commonwealth having spent many years working closely with the next generation of Commonwealth leaders. The theme of the Commonwealth for 2020 is ‘Delivering A Common Future: Connecting, Innovating, Transforming', placing emphasis on youth, the environment, trade, governance, and ICT (Information and Communications Technology) and innovation. From working to protect the earth's natural resources and preserving the planet for generations to come, to championing fair trade and empowering the youth of today to transform the communities of tomorrow, the Service celebrates the Commonwealth's continued commitment to delivering a peaceful, prosperous and more sustainable future for all. Photo © PA

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The pair are estimated to have a joint fortune of £20 million and are currently living in a mansion in Montecito, California, which they bought through a company registered to the address of Meghan's business manager.

"If Harry's been in the US for 183 days straight then he's done. But it is safe to assume they have had lawyers and tax experts grinding away on this issue for months" said Holtz.

The visa which Harry is on is a key factor, if he arrived in the country on a diplomatic visa, he is exempt, but if it was a 0-1 visa for people with "extraordinary abilities", then he will be liable for the same taxes in the US as everyone else.

"Meghan is a US taxpayer and her situation hasn't changed, but Harry will have to tell the IRS about every penny he has received. That includes paying gift tax on any monetary gifts he received from Prince Charles and he will have to show any other source of income including trust funds set up after the death of Princess Diana" said another accountant.