The coronavirus lockdown, coupled with the months-long closure of the royal palaces, has threatened to blow a A$33.6 million ($36.28m) hole in the Queen's finances.
According to an exclusive report from The Sun, an email to staff from the head of the Royal Household, Lord Chamberlain Earl Peel, warned there could be a $35.84m shortfall – a third of the annual royal income – and employees could face a pay freeze and job cuts.
Visits from millions of tourists to Buckingham Palace each year rake in roughly $24.18 million per year for the Royal Family from ticket and souvenir sales; while visits to Windsor Castle earn them around $50.31m each year.
"The crisis has already tested our resilience, adaptability and preparedness in many ways and at all levels across the organisation. It has also had a significant impact on the activities of the whole Royal Household," the email read.
"Although the UK appears to be over the peak of infections, it remains unclear when measures such as social distancing will come to an end.
"We must therefore assume it could still be many weeks, if not months, before we are able to return to business as usual.
"There are undoubtedly very difficult times ahead and we realise many of you will be concerned."
The Queen's diary, which had been planned up to two years in advance, was filled with tours by her and senior royals as well as visits to the UK from foreign heads of state.
But as a result of the Covid-19 pandemic – and the chance of life only truly returning to normal once a vaccine against the virus is widely available – all remaining investitures this year have been cancelled, and events next year and in 2022 have been placed under review.
"We just can't make any plans as we don't know what will happen. The virus has had a cataclysmic effect," one royal aide said.
"Even the staff Christmas party is in doubt," another source told the publication.
Staff, including those who work in the Buckingham Palace State Rooms, usually opened to tourists heading into the UK's summer, have been asked to work from home.
And while they're yet to lose their jobs, many have been warned they could face recruitment and pay freezes.
In his email, the Lord Chamberlain said "property spend" would also be reduced – a move that could affect planned renovations and repairs to Buckingham Palace.
"The Royal Household, like most organisations, is not immune to the impact of the pandemic on our financial position," he wrote.
"Many projects have been halted and all but essential expenditure has been suspended.
"A recruitment freeze has been implemented and no new posts will be appointed unless a very clear business case exists.
"This year's annual pay review has also been paused."
Around 500 people are employed by the Royal Household, though it's currently operating on a "skeleton staff" in many areas.
The blow comes following one royal biographer's warning that Her Majesty may never return to "frontline" royal duties if coronavirus restrictions render public engagements unsafe for longer than this year.
The Queen, 94, will remain in lockdown at Windsor Castle until at least the end of August – her longest absence from duties in her 68-year reign.
"It's terribly sad but I can't see how the Queen can resume her usual job. The Covid-19 virus isn't going away soon and will be with us for months, if not years," royal biographer Andrew Morton said, adding it was likely we'd only see her on TV or video from now on.
"It would be far too risky for the Queen to start meeting people regularly. She has always loved getting out and meeting people but she can't take the risk.
"How can she carry out investitures, meet ambassadors, do walkabouts and visit places without meeting people at close range? If she gets the bug, it could be fatal and would put Prince Philip at risk."