A bullying row which led to a former rugby boss leaving his job at Museum Wales left taxpayers with a bill of more than £620,000, a report has said.
Roger Lewis was the subject of complaints from two senior employees when he was the museum's president.
The museum has been criticised for how it settled the dispute.
Mr Lewis said an investigation had found that he had not breached any of the Nolan Principles for public life.
An account of that investigation in the report, from the Auditor General Adrian Crompton, also said that some aspects of the grievances levelled against him had been upheld, in part or full.
Mr Lewis was appointed by the Welsh government to be president of the museum from April 2019, before he recused himself in November 2022 as part of a settlement, and left on New Year's Eve 2022, three months earlier than planned.
In the month after he recused himself, in December 2022 he was appointed by the Welsh government to lead a review of heritage body Cadw.
Mr Crompton's report said the Welsh government's own investigation found his behaviour did not always reach the highest standards.
Mr Lewis is a former chief executive of the Welsh Rugby Union and former chair of Welsh government-owned Cardiff Airport.
The report said that the museum spent £757,613 including a £325,698 settlement to the then director general David Anderson, who was in charge of the organisation.
A total of £419,915 was spent on legal and professional services - although the museum was able to claim back £131,230 through insurance.
Mr Crompton raised concerns over "serious governance failures" at the institution and said it could not show how it acted in the best interests of the public purse.
Museum Wales, also known as Amgueddfa Cymru, said the report was not a "fair representation of the events that occurred".
The charity runs a network of sites across Wales including National Museum Cardiff.
According to the report, Mr Anderson and former chief operating officer Neil Wicks complained to the Welsh government about Mr Lewis in June 2021.
Mr Crompton said they alleged that some of the former president's behaviour towards them "constituted bullying and discrimination".
An independent investigator appointed by the Welsh government did not find that the president had "clearly breached the terms of his appointment".
But it said, according to Mr Crompton, that his behaviour "had not always reached the highest standards and that his actions had left him open to accusations that he had not always been as objective and open as he could have been".
Both officers had also submitted grievances to the museum itself. Mr Anderson also submitted two claims to an employment tribunal - the second in August 2022 including allegations of victimisation.
An independent investigation into the officials' grievances, from February 2023, did not find that the former president breached the Nolan Principles that public officials are expected to uphold.
Mr Crompton said it "did not uphold many of the grievances, but did uphold some aspects in part or in full", including that the former president "publicly and privately undermined the former director general, chief operating officer and other staff when meetings were called in breach of the regulations of the board of trustees".
Mr Anderson had alleged that the trustees of the museum were meeting in closed sessions without officers being present.
The museum began a mediation process with the then-director general in October 2022, which led to a settlement that saw the tribunal claims withdrawn.
The agreement saw Mr Anderson put on a notice period until September 2024 - he is now Emeritus Fellow of the Museum and not director general.
Mr Lewis, as a part of the agreement, recused himself from his role from 17 November 2022 and stepped down on 31 December that year, three months before he scheduled end of his term.
The agreement was signed by the Welsh government's director of human resources, the museum's vice president, Mr Lewis and Mr Anderson.
The Welsh government largely funds the charity using public money and also appoints Amgueddfa Cymru's president.
Mr Crompton found the "decision-making process concerning the resolution of the employment dispute with the former director general was fundamentally flawed".
He said the museum had not been able to demonstrate it acted in the best interests of the charity or that the settlement represented value for money.
He said his audit team was also not provided "with any specific written advice from the Welsh government to Amgueddfa Cymru concerning the settlement agreement itself, notwithstanding the involvement of the Welsh government's director of human resources in that process".
Mr Wicks himself retired at the end of July 2022 and received a payment of £12,000 to settle any potential claim with the museum. The auditor general did not identify concerns with the decision making process around that payment.
Mr Lewis said: "I am reassured to note, that the auditor general in his report stated twice that during my tenure of office as president of Amgueddfa Cymru, that I had not breached any of the Nolan Principles, the "Seven Principles of Public Life", and the auditor named them: selflessness, integrity, objectivity, accountability, openness, honesty, and leadership."
In a statement the museum said: "Amgueddfa Cymru respects the auditor general's opinion and recommendations and has appreciated the engagement with Audit Wales throughout this difficult process.
"However, we are disappointed that some of the evidence provided by Amgueddfa Cymru has not been reflected in the report.
"As a result, we do not feel it a fair representation of the events that occurred or fully considers the complicated circumstances which Amgueddfa Cymru had to resolve."
It said the settlement "enabled the museum to avoid what would have been long and protracted legal processes and the associated costs".
"The figure of £757,613 represented in the report does not represent the settlement figure alone but includes contractual salary costs, professional fees incurred over a period of several years."
It said it had "taken a number of learnings from this difficult period".
A Welsh government spokesperson said: "We are aware of the Audit Wales report and recent governance issues at Amgueddfa Cymru.
"We will carefully consider the report's conclusions before responding."
The Senedd's public accounts and administration committee raised its own questions about "the Welsh government's management of its arm's length bodies" saying that the committee "will be demanding answers from the Welsh government about its involvement in the saga, as well as questioning the new chair and chief executive about restoring stability and driving improvements at the museum".