The departing US ambassador, Ms Jean Kennedy Smith, was taken by surprise at her farewell party when the Taoiseach, Mr Ahern, announced that she would be made an honorary citizen of Ireland.
The honour was kept a secret until the Taoiseach's speech at the ambassador's residence on Saturday night, when he said he wished to mark the occasion by some recognition of the immense service she had given.
More than 2,000 people gathered for the American Independence Day party. The arrival of the guests caused traffic jams along the main road in the Phoenix Park. The dress code was that everybody should wear red, white and blue. The Taoiseach wore a blue suit and a red tie.
Guests were entertained by three Irish tenors, Niall Morris, Joe Conlan and James Nelson, as well as by the Army No One Band and a US navy band. Defence Forces parachutists, with Irish and US flags on their parachutes, landed on the lawn.
Guests, who included Ministers, politicians from all parties, diplomats, civil servants, senior churchmen and business people, were catered for in a marquee to burgers, hot-dogs, American beer and red and white wine, before the speeches and a message from President Clinton. The evening ended with a fireworks display.
Mr Ahern announced the honour at the end of his speech. "I and my colleagues in Government wish to mark the occasion of ambassador Jean Kennedy Smith's departure from these shores by some special mark of recognition for the immense service that she has given.
"It would, accordingly, be our intention that upon the cessation of her ambassadorial role in this country, she will become an honorary citizen of Ireland, an honour that is given to very few, and the Government have accordingly made a decision to advise the President to exercise the power she has in that respect.
"I would like to thank you, again, ambassador, for all you have done for peace. You have helped to bring about a better life for everyone of all traditions throughout Ireland."
Thousands of people crowded the seafront and streets of Dun Laoghaire at the weekend for July 4th celebrations which included a re-enactment of American civil war battles, a wagon train, a parade led by Ms Kennedy Smith and an air display involving US aircraft.