More than 20,000 people could attend the Diamond Jubilee celebration for the Queen at Stormont - more than double the number previously forecast for the Northern Ireland event.
This confirmation comes after Sinn Fein claimed it was not told of the plan, which is believed to have disrupted delicate talks on a potentially historic meeting between the Queen and Martin McGuinness.
There was speculation a meeting between the two could take place at Stormont where Sinn Fein leads the power-sharing government alongside the Democratic Unionists.
But it is understood that it would be more difficult for republicans to agree to the encounter if it took place against the backdrop of such a major celebration of the Queen's reign.
The Northern Ireland Office (NIO) last week announced it was making 10,000 tickets available to the public so they could join invited guests from a number of organisations attending the event.
But it has now been confirmed that the list of invited guests is itself 10,000 strong.
Sinn Fein has predicted the jubilee bash could eventually draw as many as 25,000 royal supporters.
Fresh tensions have also emerged over the handling of the issue, after Secretary of State for Northern Ireland Owen Paterson said all political parties were aware of the "broad outline" of plans, but Sinn Fein again denied it was told of the large scale celebration.
Mr Paterson said: "I was not in the actual meetings, but all parties have been informed of the broad outlines of the visit."
Sinn Fein denied claims it knew about the event being planned by the Northern Ireland Office (NIO). A spokesman for the party said: "Neither Owen Paterson or the NIO told Sinn Fein of plans for between 10,000 and 25,000 people holding a jubilee event in the Stormont estate."