Six years after leaving the UK for a new life in America, Prince Harry and Meghan Markle are reportedly preparing to return. Exactly how long they plan to stay remains unclear, but the financial question surrounding their move may be even more intriguing than the reasons behind it.

The couple are understood to be planning for their children, Archie and Lilibet, to attend school in the UK from September. At the same time, they appear to be keeping their sprawling Montecito estate, suggesting that any return may not be permanent.

That raises an obvious question: how can the Sussexes afford to maintain homes and a lifestyle on both sides of the Atlantic?

A costly collection of homes

The couple’s California property is already a significant financial commitment.

Their 16-bedroom Montecito mansion reportedly includes a tennis court, swimming pool, gym, sauna, five-car garage and rose garden. The annual cost of running the property is said to be around £1.5million once energy, staff, gardening, maintenance and other expenses are taken into account.

Then there is their property in Portugal. The holiday home, situated on an exclusive golf and ocean complex on the country’s west coast, reportedly cost £6.3million.

It is unlikely to be a property that can simply be locked up and left unattended. If the Sussexes spend extended periods away, they may need staff to look after and maintain it.

The complex itself comes with substantial costs. Joining is reported to require an upfront fee of approximately £150,000, followed by annual service charges of around £30,000.

And now, if the family is indeed returning to Britain, there will be another property to consider.

With a royal grace-and-favour residence apparently unavailable, Harry and Meghan are expected to rent or buy a home of their own. The Cotswolds has emerged as a likely destination, fitting with the area’s appeal among wealthy celebrities and members of the Royal Family.

The Cotswolds lifestyle comes at a price

The area is home to a long list of famous residents, including David and Victoria Beckham, Ellen DeGeneres, Kate Moss, Amanda Holden, Ellie Goulding and Calvin Harris. Princess Anne and King Charles and Queen Camilla are also associated with the region.

If Archie and Lilibet attend private school as day pupils, their education could cost around £60,000 a year for the two children, rising to approximately £100,000 if they were eventually sent as boarders.

Then there are the lifestyle expenses.

Meghan is likely to have access to some of the Cotswolds’ most exclusive establishments, including members-only Soho Farmhouse, overseen by her friend Markus Anderson, and the luxury farm shop and health club Daylesford.

Membership and visits to such places are unlikely to be inexpensive, adding yet another layer to the family’s annual spending.

Taken together, the costs of maintaining several properties, educating two children privately, employing household staff and continuing their preferred lifestyle would quickly become substantial.

Harry’s inheritance

Harry does have considerable personal wealth.

When Princess Diana died in 1997, she left William and Harry approximately £6.5million each. The money was invested on their behalf by the Royal Family’s financial advisers.

By the time Harry received the full amount on his 30th birthday, his inheritance had grown to around £10million.

For most people, £10million would represent an enormous fortune. But that sum can look very different when set against the expenses associated with the Sussexes’ current lifestyle.

The Montecito estate alone reportedly costs around £1.5million a year to operate. Add their Portuguese property, a potential British home, private education, staff and other expenses, and a substantial fortune could be depleted surprisingly quickly.

There are also two particularly expensive areas that have yet to be included in that calculation: security and legal bills.

A £9.54million legal bill

Harry has spent considerable sums pursuing legal cases over security and privacy.

Most recently, he and others lost their “invasion of privacy” case against Associated Newspapers. The judge ordered them to pay a preliminary £9.54million in costs to the publishers of the Daily Mail by Friday.

Whatever the couple’s overall wealth, a bill of that size is significant.

It also comes at a time when the Sussexes’ regular sources of income are less obvious than they once were.

There have been reports about Meghan’s possible return to acting. If the rumours about her appearing in the next series of Netflix’s The Gentlemen prove accurate, the resulting fee would still need to be considered against the scale of the couple’s existing expenditure.

So where is the money coming from?

That remains unclear.

The Sussexes have valuable assets and have earned substantial sums through commercial ventures, but the cost of maintaining their properties and lifestyle, combined with private schooling, security and legal expenses, creates a considerable ongoing financial burden.

Their decision to return to Britain has therefore created two major mysteries.

One is why Harry and Meghan have chosen to come back after Harry said last year, “I can’t see a world in which I would bring my wife and children back to the UK at this point.”

The other is how they intend to finance a life that could involve expensive homes and commitments in both Britain and America.

For now, the answer to the financial question is no clearer than the reason for their sudden return.