The charity watchdog is reviewing information about donations to The Prince of Wales's Charitable Foundation amid reports that Prince Charles was handed €3million in cash stuffed into bags by a Qatari sheikh.
The payments were allegedly accepted by the heir to the throne during private meetings between 2011 and 2015, The Sunday Times reported.
Now the Charity Commission, which regulates charities in England and Wales, says it is aware of the reports about donations and is looking into the matter.
It said: "We will review the information to determine whether there is any role for the Commission in this matter."
Charities are allowed to accept donations in cash.
Clarence House insists all correct processes were followed over the donations from Qatar's former prime minister Sheikh Hamad bin Jassim bin Jaber Al Thani, known as HBJ, The Sunday Times reported.
A spokesman said: "Charitable donations received from Sheikh Hamad bin Jassim were passed immediately to one of the Prince's charities who carried out the appropriate governance and have assured us that all the correct processes were followed."
The three lots, which totalled €3m, were handed to the prince personally between 2011 and 2015.
It is claimed that on one occasion, Sheikh Hamad, 62, presented the prince with €1m reportedly stuffed into carrier bags from Fortnum & Mason, the luxury food store that has a royal charter to provide the Royal Family with groceries.
The cash payments were deposited into the accounts of the Prince of Wales's Charitable Fund (PWCF), an entity that bankrolls the prince's private projects and his country estate in Scotland, it added.
There is no suggestion anything about the payments was illegal.
It is the latest claim to beset the future king who is currently in Rwanda representing the Queen at the Commonwealth Heads of Government Meeting.