Harry and Meghan could be facing a $5 million bill for private security if they lose their publicly-funded protection officers, according to a bodyguard dubbed the Secret Service of Hollywood.

Force Protection Agency founder Russell Stuart, who helps guard stars like Jennifer Lopez and Post Malone, estimates the cost of keeping the couple and baby Archie safe going forward could run in the millions.

And he warns that this 'transitional' period announced by the Queen on Monday in the wake of the couple's decision to quit Royal duties is the most fragile time for their security, as 'it offers the bad guys an opportunity'.

Stuart, who founded FPA in 2017 and is a former California State Guard officer, told the DailyMail.com: 'They will each need between two to four guards with them at all times. Every residence they class as a home will also need to be permanently looked after.

'You are looking at a security bill totaling millions, somewhere between $3 to $5 million. Even if they become private citizens the idea that they could pop to the grocery store - that is probably never going to happen.'

Her Majesty, 93, broke with protocol to refer to the couple by their first names rather than the 'Duke and Duchesss of Sussex' on Monday, suggesting they are poised to be stripped of their HRH titles as they split their time between Canada and the UK.

Harry and Meghan are facing a $5 million bill for private security if they lose their publicly-funded protection officers, according to a bodyguard dubbed the Secret Service of Hollywood

Prince Harry Leaves The True Patriot Love Symposium surrounded by his Canadian security detail in 2017. Canada's finance minister Bill Morneau has already said its government has not yet decided if it will cover the estimated $1.7 million it currently costs to provide round-the-clock protection for Harry and Meghan

A-listers, sports stars and high net-worth individuals, including Mariah Carey, Diddy, Linkin Park and Kelly Clarkson all currently use Stuart's agency. They are based in Beverly Hills with offices in New York, Florida and a new office opening in London.

Harry and Meghan are currently entitled to 24/7 taxpayer-funded protection at home and abroad as members of the royal family.

Buckingham Palace, the UK Cabinet Secretary Sir Mark Sedwill and the Home Office have already discussed the future of the couple's security.

Stuart added: 'Even someone like Beyonce or Jay Z - the attention they receive is no where near close to the type of media scrutiny as the royals get.

'For that reason their security would be on incredibly high alert. They are global figures which means they would need the highest level of security at all times and everywhere they go. There are two of the most famous people on the planet.

'Because of that running their security detail comes with an incredible amount of pressure and its own set of additional problems.

Force Protection Agency founder Russell Stuart, who helps guard stars like Jennifer Lopez and Post Malone, estimates the cost of keeping the couple and baby Archie safe going forward could run in the millions

'And they will need security now more than ever. There are a lot of bad people in the world. Any transitional period would offer them an opportunity.

'The moment that they might see people are stepping away or there is a change they might think this is their shot. This is the time where their security needs to be at its highest, right now.'

Stuart says the biggest part of keeping any A-lister safe is 'in the planning', adding: 'Certainly extra bodies and technology help but it is all in the planning in where that famous face wants to be and when.

'Of course everyone will approach it differently and of course it will depend on the number of people they use but they will need 24 hours a day, seven days a week care.'

Canada's finance minister Bill Morneau has already said its government has not yet decided if it will cover the estimated $1.7 million it currently costs to provide round-the-clock protection for Harry and Meghan.

It follows reports that Prime Minister Justin Trudeau had already promised the Queen that Canada - and its taxpayers - would help pay for the couple's security.

Trudeau also assured the Queen that the family would be safe while in his country with Canada expected to pay around half of the estimated $1.7 million annual security bill, London's Evening Standard claimed.

But Morneau told reporters in Toronto on Monday: 'No, we haven't spent any time thinking about this issue. We obviously are always looking to make sure, as a member of the Commonwealth, we play a role. We have not had any discussions on that subject at this time.'

Stuart's agency is based in Beverly Hills with offices in New York, Florida and a new office opening in London. Stuart is pictured with partner Mike Fairbanks

A-listers, sports stars and high net-worth individuals, including Jennifer Lopez, left, Post Malone, right, Mariah Carey, Diddy and Kelly Clarkson all currently use Stuart's agency

Stuart founded FPA in 2017 and is a former California State Guard officer

The Queen's statement in full after a day of talks to decide the futures of Harry and Meghan

Stuart does not think the couple will lose their public protection, at least not in the immediate future.

He told DailyMail.com: 'I do not think they will remove the royal security protection. I imagine it will be a similar position to that when a president is no longer in the tole. He or she will always have secret service protection.

'That being said we would love to be able to offer our services to the couple. The level of constant attention from both the public and the media is unlike any celebrity.'

The Queen on Monday agreed to allow her grandson and his wife to split their time between Canada and the UK while an agreement was made on their future following their shock resignation as senior royals.

Asked about the issue of who will fund their security, the British Home Secretary Priti Patel told the BBC: 'I'm not going to provide any detailed information on the security arrangements for either them or any members of the Royal Family or for any protected individuals - that's thoroughly inappropriate for me to do so.

'At this moment in time, right now, the royal family themselves need some time and space for them to work through the current issues that they're dealing with.'

The couple will need each need between two to four guards with them at all times and every residence they class as a home will also need to be permanently looked after, Stuart says. Meghan and Harry are pictured with son Archie in September last year

The Queen said on Monday that she'd held 'very constructive' talks with Harry, his brother Prince William and their father Prince Charles in a bid to chart a course through the fallout of the bombshell announcement.

'My family and I are entirely supportive of Harry and Meghan's desire to create a new life as a young family,' the 93-year-old monarch said in a statement after the first day of meetings at her Sandringham estate in eastern England.

Harry and Meghan said they wanted to 'carve out a progressive new role within this institution'.

The monarch stressed the couple told her 'they do not want to be reliant on public funds' but did not address the issue of whether they would keep their royal titles.

A Trudeau spokesperson declined to comment on whether Canada's taxpayers would foot the bill. There have been concerns that the large cost of providing security for Harry and Meghan could lead to a backlash in Canada and damage the status of the monarchy there.