King Tuheitia's wife and son flew to Washington DC to attend the annual National Prayer Breakfast with President Barack Obama and associated events last month at a cost of $64,360.
A leaked travel bill from Orbit Corporate Travel was invoiced to "Ururangi Trust" - the body that handles an annual $1.28 million grant given to the King by Waikato-Tainui.
The bill is for Atawhai Paki and her son Whatumoana who, according to an email sent to the Herald via former broadcaster David Beatson, are also known as Te Makau Ariki Atawhai and Te Ariki Tamaroa Whatumoana.
Mr Beatson is a director of Ururangi Ltd, a company linked to Ururangi Trust. He is also stepfather of Greg Miller, a spokesman for the King.
Mr Miller said the travel arrangements were made through Ururangi for administrative reasons, but the trip was personal and the King had always intended to repay costs.
Asked if the costs had been reimbursed, Mr Miller said the media had received the bill before Ururangi Trust. The bill was a "consolidated invoice" that represented a range of expenses.
He declined to provide a copy of rules on when costs have to be reimbursed.