"Everything is an open book, and the Charities Service are welcome to come and look in," he said.
Waikato-Tainui chief executive Donna Flavell told the Weekend Herald she had nothing to say about the probe.
"It's got nothing to do with you. We're working through it ourselves," she said.
The Ururangi Trust has previously drawn the attention of Internal Affairs, and a damning 2015 report obtained by the Weekend Herald into mis-spending by the King's office and saw the trust issued with a formal warning notice.
That report, obtained by the Weekend Herald, 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.
"The transactions are not sporadic or intermittent in nature. They are repetitive, ongoing and consistent," investigators concluded of the personal spending.
But the Charities Service declined to impose its harshest sanction, de-registration of the charity, largely on representations made by Ururangi's respected chairman Sir John Goulter.
Sir John told investigators he'd taken steps to reform an office he said was tainted by "bros employing bros".
"Sir John Goulter brings a formidable reputation along with him to the Trust and Charities Service is of the view that the kinds of mistakes of ignorance he clearly admits have occurred in the past would not occur under his watch," the report concluded.
But one month after investigators closed the file on the earlier complaint, Sir John resigned from the Ururangi board. He did not return repeated calls from the Weekend Herald this week.
Fellow former trustee Traci Houpapa, who departed the Ururangi board at the same time as Sir John, said: "We asked to stand down, because they [the King's office] wanted a change of governance."
The current board of Ururangi comprises Hamilton accountant Rogers and Helen Kouta, who is the ex-wife of the King's chief of staff Rangi Whakaruru.
The Kiingitanga recently gained profile after King Tuheitia Paki made a rare entry into national politics this election cycle by formally endorsing the Maori Party and its candidates.
The effect of this endorsement has been unclear, with Maori Television last week reporting a poll of the Hauraki-Waikato electorate seat showed Rahui Papa - the King's adviser and Maori Party candidate - trailing with only 20 per cent of the vote, compared to 78 per cent for incumbent Labour Party MP Nanaia Mahuta.