A photographer shouted: "Everybody wave at the camera," and everybody waved, including the President and her husband, Martin.
It looked like a family album snap of a clan get-together, but the gathering on the front porch of Aras an Uachtarain was instead the first group of people to go on the inaugural Saturday public tour of the building.
The free guided tours, which will take place throughout the year, were initiated by the President, Mrs McAleese, to make the "people's house as open as possible", said her spokeswoman.
Some 600 visitors will be able to see the house every Saturday on a walk-in basis between 9.45 a.m. and 4.30 p.m.
Previously, group public tours of Aras an Uachtarain were available only by pre-booking.
The first group of 25 visitors did not know in advance that they would each receive a handshake and cead mile failte from the President and her husband. But some lost no opportunity in maximising their good fortune by asking Mrs McAleese to autograph their visitors' guides.
Then they set off on the 30minute tour of the main State rooms under the enthusiastic guidance of Ms Claire Ginnetty, one of three guides, and the detached glances of the Garda officers.
They "oohed and aahed" at the large dining table in the state dining room around which the members of the first government of the Irish Free State had their first meeting.
They admired the high-relief gilded rococo ceiling in the Council of State room, which depicts Aesop's Fables. They cooed over the faded black-and-white photograph in the President's study of herself as a fair-haired child.
No press photographs were allowed of the President's study, which a spokeswoman said was not previously open to public visitors.
The journalists scanned the book-shelves to see if there were any copies of Mills and Boon romances which the President did not want recorded for public consumption. But the only titles which could be read from within the roped-off area were Spanish dictionaries and books on the Troubles and the Famine.
The President's spokeswoman said no photographs were allowed of the study, because it was "nicer" for them to be taken only when the President was seated in it.
Meanwhile, down at the visitors' centre where the tours began with a 10-minute video, Mrs McAleese's 13-year-old son, Justin, was carrying a walkie-talkie and helping the organisers.
Mrs Carmel Watts from Dunboyne, Co Meath, who had brought her husband, Stephen, on the tour as a 70th birthday surprise, said she could easily spend seven years in the house.
"All of it was lovely," she said. "The fact that the public was invited here was wonderful. It's been closed for so long, but maybe that's Ireland opening up. It's great to see it in our day. I'm 52 and I didn't think I would ever see inside the Aras."