Here is part, of full Report on Duchies explains ownership.
The two Duchies are not the private property of the Windsor
family. They never have been. Yet they provide Charles and
William personal incomes in excess of £23m a year each.
£27.4m for Charles in 2024.
That’s as much as six times the
combined salaries of all elected heads of state in Europe for
William, and again for Charles. Charles’s income was one
hundred and fifty-nine times that of the prime minister.
While the royals continue to refer to them as private estates,
the Duchies of Lancaster and Cornwall both belong to the
Crown, a state institution. The King was not allowed to own
private property until 1800, hundreds of years after the
Duchies were formed. The analysis below shows clearly the
weight of evidence that shows unequivocally the state
ownership of both Duchies.
The 1337 Charter which established the Duchy of Cornwall was
clear from the outset that it was only for the use of the heir
who was also the eldest son of the monarch. It wasn’t the
personal property of the monarch’s son but held by the Crown
for heirs of the future. It was indivisible from the Crown, not
from the man on the throne or the current duke.
Likewise, when Edward VIII was forced to abdicate, in part
due to his sympathies with the Nazis, he did not retain
personal ownership of the Duchy of Lancaster. The revenue
was paid instead to his brother, the new king, while the Duchy
of Cornwall reverted to the Crown as the new king had no sons.