The Prince of Wales’s former closest aide coordinated with “fixers” in a bid to land an honour for a donor to one of the future king’s charities, an independent investigation into the royal cash-for-honours scandal has found.

Michael Fawcett, who resigned as the Prince’s Foundation’s chief executive after a string of allegations, was also involved in directing money from a Saudi billionaire’s charity to another organisation of which Charles was patron, the inquiry found.

The independent investigation into fundraising practices was ordered by the foundation and carried out independently by auditing firm Ernst & Young.

It found evidence of Fawcett’s “communications and coordination” with “so-called ‘fixers’ regarding honorary nominations for a donor between 2014-18” but trustees were not aware at the time of this correspondence.

A summary published by the Prince’s Foundation said: “With respect to the allegation of securing honours for a donor in exchange for donations, there is evidence that communication and coordination took place between the CEO at the time and so-called ‘fixers’ regarding honorary nominations for a donor between 2014-18. There is no evidence that trustees at the time were aware of these communications.”

A summary of the findings also revealed that Fawcett and another unnamed senior employee were involved in directing a transfer of funds from the Mahfouz Foundation to the Children and the Arts Foundation (Cata), which is now defunct.

The activity, including written correspondence, took place without the knowledge or approval of the Prince’s Foundation trustees, according to the investigation.

The Charity Commission has launched an inquiry into the Mahfouz Foundation, which was founded by Saudi billionaire Mahfouz Marei Mubarak bin Mahfouz, into 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 returned it to the Mahfouz Foundation.

Fawcett was subsequently involved in directing a transfer of funds from the Mahfouz Foundation to Cata, the summary said.

The findings of the Ernst & Young report, released on Thursday, will be shared with the Office of the Scottish Charity Regulator (OSCR), which is examining dealings at the foundation.

A Clarence House spokesman said the prince was grateful to independent auditors for reviewing procedures. He added: “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.”

Dame Sue Bruce, chair of the Prince’s Foundation, described the recent crises surrounding the charitable organisation as a “difficult chapter”, but said “lessons will be learned” to ensure the charity always acts with the “utmost integrity and probity”.

She said: “The board of trustees agreed unequivocally that the recent allegations had to be independently investigated so that the facts could be established, and all necessary steps could be taken to address the issues identified.

“Now that the board has the findings of the investigation, trustees are considering them in conjunction with OSCR and other relevant parties.

“The board of trustees is determined that lessons will be learned to ensure that, in future, our charity maintains the highest standards in all areas and always acts with the utmost integrity and probity.

“As we move through this difficult chapter, I hope that the stories of note will begin to focus once more on the beneficial outcomes delivered by the Prince’s Foundation, and we look forward with optimism to continuing to deliver our charitable activities.”

Other findings from the probe included that there was no evidence that employees or trustees of the foundation were aware of private dinners being sold or arranged in exchange for money.

Clarence House has previously said it had “no knowledge” of the practice of paid intermediaries arranging access to the royal family or honours in exchange for donations to the prince’s charities.

As well as Fawcett stepping down, Douglas Connell, the chair of the foundation, resigned, citing evidence of possible “rogue activity” and “serious misconduct” of which he said he had no knowledge.