US President Joe Biden has declared "I'm at home" as he made an historic address to the Irish Parliament.
Mr Biden said he has returned to his ancestral home and his only wish was that he could stay longer.
In his speech to a joint sitting of the Oireachtas (both houses of the Irish parliament), he spoke of his pride in his Irish roots and support for the peace process in Northern Ireland.
He said the UK "should be working closer" with Ireland to support NI.
President Biden's final engagement on Thursday was a banquet dinner held in his honour at Dublin Castle.
The event, hosted by Taoiseach (Irish prime minister) Leo Varadkar, involved a reception in the Portrait Gallery followed by a dinner in St Patrick's Hall.
Welcoming Mr Biden at the banquet dinner, Mr Varadkar said that both the US and Ireland have "a similar past and philosophy", one where they "are joined by bonds of kinship as well as of friendship".
"By looking always to the future, you have helped us to move beyond the past, and build something better," he said.
President Biden received a standing ovation as he once again spoke about the special relationship between Ireland and the US.
He recounted one of his grandfather's favourite sayings as he took centre stage at the banquet: "If you're lucky enough to be Irish, you're lucky enough," he said.
The president told those gathered in Dublin Castle that he felt incredibly lucky to be so warmly welcomed by so many people on his visit to the island of Ireland.
"No barrier is too thick or too strong for Ireland and the United States of America," Mr Biden said, adding: "There is nothing the two nations cannot do when they do it together".
During an earlier address in Leinster House, President Biden praised the "huge strides" that have been taken since the signing of the Good Friday Agreement in 1998, which largely ended decades of violent conflict in Northern Ireland.
"People of Ireland, it's so good to be back in Ireland," he told the Oireachtas, making a remark in Irish which translated as: "I am home."
Mr Biden went on to say that the United States was "shaped by Ireland".
"As nations, we have known hardship and division, but we have also found solace and sympathy in one and other."
'Peace is precious'
President Biden praised the Good Friday Agreement which, he said, had ensured that an "entire generation of young people's lives have been shaped by confidence that there are no checkpoints on their dreams".
He said the agreement not only changed lives in Northern Ireland, but it also had a "significant positive impact across the Republic of Ireland as well".
"Political violence must never again be allowed to take hold on this island," Mr Biden told those present, to rapturous applause.
"Peace is precious. It still needs its champions. It still needs to be nurtured," he said.
Former Irish president Mary McAleese, former taoiseach Bertie Ahern and Marie Heaney, the widow of the late poet Seamus Heaney were among those in attendance.
Stormont leaders such as Sinn Féin's Michelle O'Neill, the SDLP's Colum Eastwood and Naomi Long from Alliance were also there.
Joe Biden was the fourth US president to ever address the Irish parliament after John F Kennedy, Ronald Reagan and Bill Clinton.
He began his working day with a visit to Áras an Uachtaráin - the home of the Irish president in Phoenix Park.
President Biden inspected a military guard of honour, and signed the visitors' book. He also planted an oak tree and rang the Bell of Peace.
The bell was erected in 2008 to commemorate the tenth anniversary of the Good Friday Agreement.
After ringing the bell, President Biden gave it another ring, saying: "One more for peace".
He said he was feeling "great" and that he had "learned a lot from the president".
President Higgins then gave President Biden a quick tour of the grounds around his official residence and introduced him to one of his dogs.
The two men discussed the importance of the meeting 25 years on from the Good Friday Agreement, the strong connection between their two countries and their shared love of Irish poetry.
President Biden then met Leo Varadkar at nearby Farmleigh House, shaking hands and exchanging a few words before posing for pictures.
Mr Biden remarked that it was "a beautiful day", the weather a contrast to the conditions that greeted him as he arrived in Dublin on Wednesday.
Mr Varadkar said it was "great" to have the US President back in Ireland and that the visit was going "very well".
Mr Biden described the meeting as an opportunity to make "tremendous progress".
He said he was not just commemorating the 25th anniversary of the Good Friday Agreement - but also wanted to hail Ireland's "leadership" on world issues such as taking in Ukrainian refugees.
Earlier, Mr Biden said he had quoted an Irish proverb, in his message in the visitors' book - "your feet will bring you where your heart is", adding that it was "an honour to return".
He made a reference to returning to the home of his ancestors, pledging to recommit to peace, equity and dignity.
Mr Biden added: "I'm not going home. Isn't this an incredible place, all you American reporters, it's just like the White House, right?"
A delegation attending the event included Tánaiste (Irish deputy prime minister) Micheál Martin, US Secretary of State Anthony Blinken and former Irish football star Paul McGrath.
On Friday, the US President is expected to travel to County Mayo where he will again explore his Irish ancestry.
His great-great grandfather Edward Blewitt left Ireland around the time of the famine.
While in the county, the President, who is a Catholic, is also expected to visit shrine at Knock and to make an outdoor speech to people in Ballina before he ends his four-day visit to the island.
A US genealogist who researched Mr Biden's lineage had estimated he is "roughly five-eighths" Irish.
His great-great grandfather Owen Finnegan left there for America in the late 1840s.
Declan Harvey and Tara Mills explore the text of the Good Friday Agreement - the deal which heralded the end of the Troubles in Northern Ireland.
They look at what the agreement actually said and hear from some of the people who helped get the deal across the line.
Source: BBC