Peter Phillips' company was paid £750,000 for Queen's party
A company run by the Queen's grandson, Peter Phillips, was paid £750,000 for organising an event last year to celebrate the monarch's 90th birthday.
The Patron's Lunch - held in June on The Mall - was a street party for the 600 charities and other organisations that have the Queen as Patron.
It was the idea of Mr Phillips, but the event was not put out to tender.
Royal officials said at the time that it was a "unique proposal" that had been subjected to due diligence.
The tickets, which were given to charities connected to the Queen, cost £150 each.
There was also private sponsorship but the ticket price raised some eyebrows.
A similar reaction might have greeted the size of the fee that was paid to Mr Phillips' company, SEL Ltd.
It was not disclosed at the time of the birthday festivities because, the Queen's grandson argued, it might have an adverse effect on future business.
The £750,000 payment - now in the public domain through accounts filed with Companies House - was almost double the amount the lunch raised for good causes.
Sir Stuart Etherington, chairman of the Patron's Fund charity, which had ultimate control of the event and awarded the contract to SEL UK, defended the payment.
He said something on the lunch's scale could not be run without incurring some costs and Mr Phillips' company had made no profit.
"In addition, we compared their costs to those of other suppliers for organising the event, arranging logistics and security, and raising commercial sponsorship, and we satisfied ourselves that they were competitive in every regard," he said.
A Buckingham Palace spokesperson told the BBC: "The Patron's Lunch was an enjoyable and celebratory event which has directly benefitted a large number of Her Majesty's charities.
"Questions about the organisation and financial management are rightly a matter for The Patron's Fund Board of Trustees."
The lunch raised £384,000 before tax.
But the benefit to charities comes not only in the form of the money left over after the Patron's Lunch, but other donations.
In all, £750,000 is being given to 290 charities in the UK and the Commonwealth.