Prince Charles inspects bread made for his Duchy Originals range
The Prince of Wales' income is provided by the Duchy of Cornwall and it puts him among the UK's top earners.
King Edward III set up the duchy in 1337 for his son, Prince Edward, and it has continued to provide an income for the heir to the throne for almost 700 years.
Last year, Clarence House's first review of Prince Charles' work and accounts showed the duchy generated £11.9m.
Finance experts say this puts the prince among the UK's top 100 earners.
The estate consists of more than 140,000 acres in 25 counties, predominantly in south-west England, including agricultural, commercial and residential property.
High-profile properties include The Oval cricket ground, in south London, and Dartmoor Prison, Devon.
The duchy also includes a financial investment portfolio.
In 2003-4, commercial properties provided 43% of the princes' income, agricultural land and forestry 30%, residential properties 14% and financial assets 13%.
The prince does not own the duchy's capital assets and is not entitled to profits from their sale, only the annual income generated by them.
He voluntarily pays income tax at 40% on his duchy income and, like William and Harry, receives no allowance from the Civil List.
The prince received £3.8m grants-in-aid from the government in 2003-4, to pay for official travel and run his residences, plus £292,000 to pay for use of military staff and overseas travel.
The Clarence House review also found the prince helped raise £100m for charity last year.
All profits from his Duchy Originals organic food range, including biscuits, sausages and bacon, go to charity.