The Prince of Wales’s former most trusted aide co-ordinated with “fixers” over honours nominations for a Saudi billionaire donor to the Prince’s Foundation an investigation into cash for honours claims has found.

Michael Fawcett, who resigned as the foundation’s chief executive after a string of allegations, was also involved in directing money from the donor’s foundation to another charity of which Charles was previously patron, it was revealed.

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.”

Republic, which campaigns for an elected head of state, said there was a “glaring hole” in the investigation concerning what Charles knew about the dealings.

Clarence House has previously said the prince had “no knowledge” of the cash for honours scandal.

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

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

Mr Fawcett resigned in November amid claims he promised to help secure a knighthood and British citizenship for Saudi billionaire Mahfouz Marei Mubarak bin Mahfouz – a donor to the Prince’s Foundation.

The investigation found evidence of Mr Fawcett’s “communications and co-ordination” with “so-called ‘fixers’ regarding honorary nominations for a donor between 2014-18”, the summary said, but trustees were not aware at the time of this correspondence.

A summary of the findings revealed that Mr Fawcett and another unnamed senior employee were involved in directing a transfer of funds from the Mahfouz Foundation, founded by Dr bin Mahfouz, to the Children and the Arts Foundation (CATA), which is semi-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 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 returned it to the Mahfouz Foundation.

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

CATA, which was formerly the Prince’s Foundation for Children and the Arts, was founded by Charles in 2006 to offer young people with little access to the arts the chance to experience theatre, music and galleries.

Companies House documents filed in September 2019 said trustees would begin the process of winding up the charity.

The Times reported last month that Mr Fawcett arranged for the transfer to CATA in September 2020.

Clarence House said Charles stopped being patron of CATA in early 2019.

Mr Fawcett was Charles’s most indispensable aide over the decades, with the prince once saying: “I can manage without just about anyone, except for Michael.”

The former royal valet quit twice before, including in 2003 when, as Charles’s personal assistant, he was accused and cleared by an inquiry of selling royal gifts, but was revealed to have accepted valuable gifts from outsiders.

Dame Sue 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 investigation 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.

It also said there was no evidence of the foundation paying commissions to society fixer Michael Wynne-Parker or Burke’s Peerage editor William Bortrick.

The foundation said: “The investigation did identify other instances of commissions being discussed or paid.

“It is not uncommon for charities to pay commission to third parties for the introduction of donors.”

OSCR said it was carefully considering the report and continuing with its inquiry “before we decide what action, if any, is required in this case”.

Former Liberal Democrat MP Norman Baker, who previously called on the Metropolitan Police to launch a criminal investigation into the cash for honours claims, said: “This statement is a diversion. There was never a suggestion the trustees were informed or aware of what happened.

“The issue is about Michael Fawcett and Prince Charles himself… The questions for Prince Charles have not been answered.”