Prince Charles's income from the Duchy of Cornwall rose to a staggering £22.2million last year, but he's expecting to see it fall by a "significant amount" next year.
In his role of heir to the throne, the Queen's oldest son is entitled to the surplus generated by the Duchy's vast portfolio of land, buildings and financial investments.
He uses the cash to fund his charity work and to support the Duke and Duchess of Cambridge, Prince Harry and Meghan Markle.
In the 2019-20 financial year, his annual private income from the hereditary estate rose by £617,000 - 2.9% - from £21,627,000 in 2018-19 to £22,244,000.
However it's likely that next year will see a huge drop in profits due to the coronavirus pandemic, the secretary and keeper Alastair Martin has warned.
He said: "The lockdown resulting from Covid-19 was only in place for one week of the financial year that this report covers.
"There is therefore very limited financial impact on these results.
"As to 2020-21, it is too early in the new financial year to be able to say with any confidence what the impact on our financial performance will be, but, despite having a particularly well-diversified asset base, we fully expect the revenue surplus to be down by a significant amount, in large part due to our trading enterprises being closed."
He added: "We have not availed ourselves of the various government pandemic support schemes but have continued to pay all staff."
Republic, which campaigns for an elected head of state, called for the Government to take control of the estate and stop the prince keeping the surplus.
Graham Smith, chief executive of the pressure group, said: "There is simply no justification for this ludicrous amount of money to be thrown at Charles when public services are stretched and local communities are impacted by the coronavirus."
"It's time the Duchy was rolled back into the Crown Estate and its income served the British people, not one prince."
He added: "We do not owe Charles a living. This nonsense has to stop."
The total worth of the Duchy's assets - amounting to more than £1 billion - has dropped by nearly £29 million.
It fell from £1,099,748,000 to £1,070,809,000, but much of the decrease is linked to valuation of the Duchy's investment property at the end of March amid the Covid-19 outbreak.
The report said valuation experts were taking into account the uncertain property market and had cited that less certainty, and a higher degree of caution, should be attached to the valuations.
The Duchy said that the volatility and uncertainty posed "no short or long term financial threat" to the asset values of its properties.
The private landed estate was created in 1337 by Edward III to support his son and heir Prince Edward, known as the Black Prince, and all his subsequent heirs.
It extends across 23 counties in England and Wales and includes the Oval cricket ground and 67,000 acres of Dartmoor.
Mr Martin said the coronavirus crisis had caused "significant personal and financial disruption" for many Duchy tenants, particularly in the Isles of Scilly and Cornwall, where the economy is reliant on tourism and hospitality.
He highlighted the uncertain future and pledged to work with the tenants to help them in the wake of the pandemic.
"It is unclear how the coming year will unfold. During this difficult and anxious time for the Duchy family, we will continue to maintain close links with all our tenants and work with them to re-establish, where possible, their livelihoods," he said.
Rent deferrals have been agreed with many tenants, he added.
The report also highlighted "legislative hiatus" over the UK's departure from the EU as having an impact.
"Uncertainty arising from this hiatus makes planning and investment decisions more complex. This is an area of deep concern for our agricultural tenants in particular," it said.
Charles uses his Duchy income to pay for his official duties, his London office and charitable work.
He also funds the public duties of Duke and Duchess of Cambridge and some of William and Kate's private costs.
He will have done the same for the Duke and Duchess of Sussex from his 2019-2020 income.
Harry and Meghan quit as senior royals in March at the end of the financial year.
At the time, it was confirmed Charles would continue to make private financial contributions to Sussexes as they began their new life in the US.
But it is not known whether this is coming from Charles' Duchy money or his other private sources such as any inheritance or private investment.
Taxpayer funding from the Sovereign Grant is used to meet the cost of Charles and the Duchess of Cornwall's official travel, and that of Cambridges.
The prince pays Income Tax voluntarily on the Duchy surplus, after official expenditure has been deducted, at the 45% rate.