Future King Prince Charles accepted a suitcase containing €1m in cash from Qatar's former prime minister "HBJ", thetimes.co.uk reported.
It said the Prince of Wales received three €1m gifts from the sheikh at undisclosed meetings.
HBJ said to give money in 500 euro banknotes.
Citing sources, the report said royal aides were uneasy, but counted cash at Clarence House.
The report further said that the cash was deposited into PWCF, a low-key foundation that controls the prince's pet projects and the country's wealth.
The publication reported that Clarence House said it was "assured" that the correct procedures were followed.
No suggestion of illegality was found, the report said.