US President Joe Biden has told elected representatives in the Republic of Ireland: "I'm at home".
Mr Biden told the Irish parliament he has returned to his ancestral home and his only wish was he could stay longer.
In his speech to a joint sitting of the Oireachtas (both houses of the Irish parliament), the president spoke of his pride in his Irish roots and support for the Good Friday Agreement.
His address in Leinster House is one of a number of events on Thursday.
"People of Ireland, it's so good to be back in Ireland," he said, making a remark in Irish which translates as: "I am home."
Mr Biden went on to say that the United States was "shaped by Ireland".
"The values that we share remain to this day - the core of our historic partnership between our people and our governments," he said.
"As nations, we have known hardship and division, but we have also found solace and sympathy in one and other."
Mr Biden said he can define the US-Ireland relationship with just one word: "Possibilities".
"There is nothing beyond our capacity if we work together. Now is the time to meet every challenge together," he said.
'Peace is precious'
President Biden praised the Good Friday Agreement, which, he said has ensured that an "entire generation of young people's lives have been shaped by confidence that there are no checkpoints on their dreams".
"Political violence must never again be allowed to take hold on this island," Biden told those present, to rapturous applause.
"Peace is precious but still needs a champion."
Former Irish president Mary McAleese, former (Irish prime minister) 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 only the fourth US president to ever address the Irish parliament after John F Kennedy, Ronald Reagan and Bill Clinton.
Later, President Biden is to be the guest of honour at a state function in Dublin Castle, the former seat of British power in Ireland.
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. The two leaders shook hands and exchanged 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.
'America and Europe working together'
Speaking afterwards, Mr Varadkar hailed the importance of both the US and European leadership, praising the vital role that the US has played in helping Ukraine since the Russian invasion last year.
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.
President Biden visited both Dundalk and his ancestral roots in the town of Carlingford in County Louth on Wednesday.
He met distant relatives in the Cooley Peninsula, where crowds lined the quayside as the presidential motorcade arrived.
Later in Dundalk, there were shouts of "welcome home, Joe" when Mr Biden arrived to address an audience at the town's Windsor Bar.
He said Irish people were the "only people in the world in my view who are actually nostalgic about the future".