The Prince of Wales's private estate is to be scrutinised by the Public Accounts Committee (PAC) as new figures show his funding from the taxpayer fell by almost 50%.
The Duchy of Cornwall, which provides heirs to the throne with a private income, will be examined by the body which has already looked at the tax affairs of Starbucks, Google and Amazon.
Charles's annual review published today showed the heir to the throne's funding from the taxpayer fell by 47% during the last financial year from £2.1 million to £1.1 million.
The large fall in spending was largely part due to a reduction in travel costs as the overseas realms - countries where the Queen is head of state - footed the bill when he visited the nations.
Spending on official travel paid for through the sovereign grant - the new funding system which has replaced the civil list - and grants-in-aid fell during 2012/13 from £1.3 million to £644,000.
It was revealed yesterday that the monarchy cost the taxpayer £33.3 million in the last financial year - an increase of nearly a million from the previous year.
Charles's income from the Duchy of Cornwall, a portfolio of land, property and investments, was up 4% to a record level of £19 million.
The Prince's tax bill fell slightly by £70,000 to £4.426 million, a drop of 1.5%.
William Nye, Charles's principal private secretary, speaking during a press briefing about the annual review, said: "Naturally we're happy to appear before the Public Accounts Committee, if they would like to see us."
He added: "The Duchy estate provides an income for the heir to the throne, there are some special rules that apply to it.
"The Prince of Wales gets the income from the Duchy but he doesn't have access to the capital, that's always been the case."
Mr Nye went on to say that Charles funds the majority of the official costs of himself and immediate family - the Duchess of Cornwall, Duke and Duchess of Cambridge and Prince Harry - and although exempt from income tax pays it voluntarily on his Duchy income.
Asked to comment on claims that the Duchy should pay corporation tax, he replied: "It's not a corporation so it doesn't pay corporation tax, it's owned by the Duke of Cornwall and he gets the income and then he pays income tax, like anybody else who owns some property from which they gain an income."
He added: "The whole point about the Duchy is that it is set up specifically, and indeed required by law, to maintain its capital, to roll over and maintain its capital and to invest in the future to generate income for the future."