President Barack Obama told three lucky schoolchildren to say cheese as they posed for photographs.
Margaret McDonagh, Colm Dunne and Onyedika Ukachukwu were left with the memento of a lifetime after being chosen to ring a Peace Bell during a tree-planting ceremony.
Mr Obama shovelled soil over an Irish oak in the grounds of Aras an Uachtarain, the official residence of President Mary McAleese, as the youngsters rang the bell.
Mr Obama told them: "You did an outstanding job. Excellent."
Onyedika, eight, is the Irish-born daughter of Nigerian parents and attends Scoil Mhuire in Blakestown, west Dublin.
Nine-year-old Colm, who is visually impaired, attends Scoil Bhride in Paulstown, Co Kilkenny.
And Margaret is a member of the travelling community. The 10-year-old is a pupil at St Francis of Assisi Senior School in Priorswood, north Dublin.
Mr Obama, his wife Michelle, Mrs McAleese and her husband Martin, chatted with the youngsters before the group posed for photographs.
"Let's get in for a picture," Mr Obama said.
"Everyone say cheese - that's what we do in the United States. We say cheese.
"It's wonderful to see you all."
The Peace Bell was unveiled in the grounds of Aras in 2008 by Mrs McAleese to mark the 10th anniversary of the Good Friday Agreement.
It has been rung on only two other occasions - the day it was unveiled and when a tree was planted by the Queen a few feet away last week.
Mr Obama's Irish oak stood about 50ft from a sequoia planted in 1963 by President John F Kennedy and close to where a tree was planted by former president Bill Clinton.