The Prince of Wales and Camilla Parker Bowles have chosen their sons as witnesses to their civil wedding.
Prince William will share witness duties with Tom Parker Bowles
Prince William, 22, and Tom Parker Bowles, 30, will share duties, Clarence House has announced.
It is now known that the Duke of York, the Earl and Countess of Wessex and the Princess Royal will all attend the ceremony despite the Queen's absence.
The private ceremony will take place at Windsor Guildhall on 8 April, followed by a televised blessing.
Registrar Clair Williams, who will perform the ceremony aided by Claire Patterson, admitted a few nerves.
"While all weddings are very special to the couples concerned, this one is particularly important and it is a tremendous honour to be a part of the occasion," she said.
Following the private wedding ceremony, the Archbishop of Canterbury will preside over the televised blessing in St George's Chapel, at Windsor Castle.
It will be attended by the Queen, the Duke of Edinburgh and about 750 guests.
Charles' godson Tom Parker Bowles, the son of Mrs Parker Bowles and first husband Andrew, made headlines in 1999 when he allegedly admitted taking cocaine.
The Prince of Wales was reported to have telephoned the then 24-year-old and given him a severe scolding.
Last month, royal aides announced that the Queen had chosen not to attend the civil ceremony because of the couple's wish for a "low key" event.
Mr Parker Bowles made headlines over drug allegations in 1999
BBC correspondent Nicholas Witchell said the reasons given now seemed "strange".
"It does make it seem that much more strange that the Queen and the Duke of Edinburgh are not attending because it is the wish of the couple that it should be low key.
"Then lo and behold, Prince Charles' two brothers, his sister and his two sons do attend."
On Tuesday, Clarence House confirmed that Mrs Parker Bowles wanted the title of Princess Consort, not Queen, when the Prince of Wales becomes King.
Her wishes were enough and legislation would not be needed on the issue, it said.
Clarence House made the statement after it was confirmed in the Commons that, unless the law was changed, Mrs Parker Bowles would be entitled to be known as Queen.