Tukoroirangi Morgan, the Māori King's former adviser, has sent him a scathing three-page letter in which he calls him a "puppet king".
Morgan, a former MP and broadcaster, said in his letter to King Tūheitia that he had no choice but to defend himself after the King publicly criticised him at an Iwi Chairs Forum dinner at Ngaruawahia recently.
"Our people see you as a 'puppet King' ... As I travel around the motu the support for Kiingitanga is in decline," he wrote.
Morgan also referred to a Serious Fraud Office (SFO) investigation into claims of financial misappropriation connected to one of the King's close advisers, Rangi Whakaruru.
Morgan said that when the King was first selected, he was "proud", but as his chief adviser he "cringed each time you stood to speak and hoped your speeches were short. There were occasions when you publicly abused people by swearing at them".
"Some of our people fear you. I don't and I never have."
King Tūheitia's adviser Sir Wira Gardiner said in a statement today: "As is well known, the SFO continues to investigate aspects associated with the King' office. Until such time as they report, we will certainly not be commenting on any such matters or allegations."
Maori Development Minister Nanaia Mahuta today said much of the letter contained issues related to the SFO investigation and she couldn't comment on those.
"The tribe is looking seriously at many of the things that were said, but many more are a matter for the Serious Fraud Office," she told reporters.
The Herald has been reporting on the issues for more than a year.
The SFO raided the office of the Māori King in July.
An earlier investigation into Ururangi Trust, responsible for funding the King's office, by the Charities Service branch of DIA had been ongoing since September 2017 but was brought to an abrupt end in June when Ururangi voluntarily deregistered itself.
Previous Herald reporting has raised concerns over whether Whakaruru used Ururangi's charitable funds to cover his $46,000 gastric band surgery at a private hospital in 2016, and also his company's use of low-interest related-party loans to cover $82,000 in non-charitable travel expenses.
Whakaruru has denied any misspending or wrongdoing at Ururangi.
At the time, Morgan welcomed the SFO investigation, and said he hoped it quickly got to the bottom of allegations.
In 2015 Ururangi was the subject of an adverse Charities Service investigation that warned further problems could see its charitable status revoked.
That report, obtained by the Herald last year, detailed the King's $350,000 annual salary and raised concerns about 114 transactions between 2012 and 2014 totalling $120,691, relating to the purchase of jewellery, clothing and beauty treatments and almost $90,000 in cash withdrawals.