Prince Charles's former closest aide coordinated with "fixers" over an honours nomination for a Saudi billionaire who donated to his charity, an investigation has found.
Michael Fawcett resigned as the chief executive of the Prince's Foundation after allegations against the ex-royal valet emerged.
He was also involved in directing money from the donor's foundation to another charity, of which Charles was previously patron, according to the investigation.
Mr Fawcett quit after being accused in newspaper reports of promising to help secure an honorary CBE and British citizenship for Mahfouz Marei Mubarak bin Mahfouz, who denies any wrongdoing.
Mr bin Mahfouz was given a CBE by Charles in a private ceremony at Buckingham Palace in 2016, The Sunday Times said.
Dame Sue Bruce, chair of the Prince's Foundation, described the recent crises surrounding the future king's charitable organisation as a "difficult chapter", but said "lessons will be learned" to ensure the charity acts with the "utmost integrity and probity".
Clarence House said: "It is important to His Royal Highness that the charities which bear his name operate to the highest standards, in accordance with rules established by charity regulators.
"We are taking this opportunity to reinforce guidance to these charities, particularly in respect of their relationships with supporters."
Clarence House has previously said the prince had "no knowledge" of the cash for honours scandal.
In September, both the Prince of Wales and Mr Fawcett were reported to the police over the cash for honours allegations.
Republic, which campaigns for an elected head of state, criticised the "glaring hole" in the investigation concerning what Charles knew about the dealings.
Graham Smith of Republic said: "How could a charity CEO acquire honours or meetings with Prince Charles without Charles's knowledge of what was going on?
"It isn't credible, but the charity has carefully steered clear of any questions about Charles, which leaves a glaring hole in their investigation."
The probe found Mr Fawcett and another unnamed senior employee were involved in a transfer of money from the Mahfouz Foundation, founded by Mr bin Mahfouz, to the Children and the Arts Foundation (CATA), which is semi-defunct. Prince Charles ceased to be a patron of CATA in early 2019.
The activity took place without any knowledge or approval from the Prince's Foundation, according to the investigation.
The Charity Commission has launched an inquiry into the Mahfouz Foundation over allegations that donations intended for the Prince's Foundation went to CATA instead.
The Prince's Foundation initially received £100,000 from Russian banker Dmitry Leus, via the Mahfouz Foundation, but Charles's charity's ethics committee rejected the money and it was returned.