Published Thursday, 14 June 2012
The Diamond Jubilee celebration will be held during the Queen's visit to NI. (© UTV)
It is more than double the figure originally estimated for the event in the grounds of the estate on 27 June.
Up to 10,000 free tickets will be available to the public on Tuesday through Ticket Master, while the same number will be made up of representatives from emergency services, ex-service associations and government departments.
The Northern Ireland Office said members of youth groups, local councils, health trusts, and Education and Library Boards have also been invited.
Earlier this week, deputy First Minister Martin McGuinness said he was "surprised" at the plans for the party and described the NIO announcement as "unfortunate".
Sinn Féin has still not confirmed whether he will shake the Queen's hand during her two-day visit on 26-27 June.
On Thursday Secretary of State Owen Paterson said all parties, including Sinn Féin, were aware of plans for the Queen's visit to Northern Ireland.
"I think all parties are aware of the general plan that was being developed, but details will emerge later," Mr Paterson said.
When asked about the handshake, he said: "That's a detail to be discussed with local parties."
He said he was not in any actual meetings but said that all parties were aware of the "broad outlines" of the planned visit.
Owen Paterson is being deliberately disingenuous in his remarks today. It is typical of the ham-fisted way the NIO has operated under Mr Paterson’s tenure.
But Sinn Féin MP Pat Doherty said Mr Paterson's comments were "disingenuous" and the event should have been discussed by the Executive.
"Neither Owen Paterson nor the NIO told Sinn Féin of plans for between 10,000 and 25,000 people holding a Jubilee event in the Stormont estate.
"This matter did not go to the Executive - in our view it should have done."