President Joe Biden has reinforced his pride in his family links to Mayo in the Republic of Ireland saying the county was now "part of my soul".

He was addressing tens of thousands of people on the final part of his four-day visit to the island of Ireland.

Mr Biden said the 25th anniversary of the Good Friday Agreement was a reminder of the importance of peace.

Taoiseach (Irish Prime Minister) Leo Varadkar said Mr Biden was "the most Irish of all American presidents".

"Thank you, for your lifelong commitment to peace on our island, your friendship, for the leadership you have shown protecting all that has been achieved, and for everything you are doing to help build a better future here, in America and in our world."

Earlier, Mr Biden had a chance encounter in Mayo with the priest who gave the last rites to his son Beau.

Beau Biden, the former Delaware Attorney General, died from brain cancer in 2015.

During a visit to Knock Shrine, the president met ex-US Army chaplain Fr Frank O'Grady who is now working there.

'We had a real reunion'

Fr O'Grady said it was a "real reunion" with Mr Biden and that he spent a "delightful 10 minutes with the president".

The priest added that he was "very surprised" when he got "a phone call to say the president wanted to see me".

"I hadn't seen him really in eight years since Beau died," he said.

"His son Hunter was there too, so we had a real reunion."

The parish priest who brought about the meeting said it was a "wonderful, spontaneous thing".

Fr Richard Gibbons told BBC Radio's Ulster's Evening Extra programme he gave President Biden a tour of the basilica at Knock Shrine and said he spoke about his family, his faith and his son Beau.

"He [President Biden] was crying, it really affected him and then we said a prayer, said a decade of the rosary for his family," the priest said.

"He lit a candle and then he took a moment or two of private time for prayer."

Knock Shrine is a pilgrimage site for Catholics. In 1879, locals said they saw an apparition of Mary, Joseph, John the Evangelist, angels and an altar with a cross and a lamb (representing Jesus).

Mr Biden, who is also being accompanied by his sister Valerie Biden Owens, has links to County Mayo through his great grandfather Edward Blewitt.

From Conor Neeson, BBC News NI in Ballina

Heavy rain has failed to dampen the mood among thousands of people gathered in Ballina ahead of President Biden's speech.

A double rainbow formed in the sky above the cathedral at one point, as The Coronas played for the crowd at an event held to welcome him.

Young and old mingled along the River Moy as the excitement started to build for the arrival of the guest of honour.

Children on the shoulders of their parents waved US flags and Irish flags.

People are draped in banners which are unlikely to keep them dry as the rain intermittently falls.

The music is keeping everyone warmed up for the main act as Mr Biden returns - this time as president.

Earlier, the president was presented with a brick from a fireplace that is the last surviving piece of his ancestral home in Ballina.

He also made a private visit to the Mayo Roscommon Hospice in Castlebar that is dedicated to his son, Beau.

The president also visited the North Mayo Heritage Centre, that works with people around the world who want to trace their ancestry from Mayo.

'Welcome home'

Ballina councillor Mark Duffy said people were eagerly awaiting the president's arrival.

"This is a homecoming event, it's a welcome home where he has family and friends in the area," he told BBC News NI.

Mags Downey Martin of Ballina Chamber of Commerce said it was "an epic, unbelievable, out of this world experience for Ballina".

"I mean you can't quantify it. You cannot say what it means for us," she said.

A star-studded line-up of Irish musicians, including The Academic, The Chieftains and The Coronas, entertained the crowd at St Muredach's Cathedral ahead of Mr Biden's visit on Friday night.

Coronas' frontman Danny O'Reilly told the BBC's Good Morning Ulster programme that the band was "buzzing" to perform for another US president, having previously played for Barack Obama during his 2011 visit.

"It's one of those bucket list things you're just happy to be involved in," he added.

The Mayo senior men's and women's Gaelic Athletic Association football teams also took to the stage in Ballina.

On Thursday, President Biden declared he was home as he made an historic address to the Irish Parliament.

'Working more closely'

He said the UK "should be working closer" with Ireland to support Northern Ireland.

On Friday, Tanaiste (deputy prime minister) Micheál Martin said he believed the remarks were an exhortation to everybody to work together.

"I think the context was clear from the president, he was speaking in the context of all of us," Mr Martin said.

"He mentions the United States, the European Union, the United Kingdom and Ireland."

Mr Martin also praised a speech the president gave in Belfast on Wednesday, saying it achieved the right balance and would help the political atmosphere in Northern Ireland.

"I think it will have served a purpose, in respect of that I have no doubt," he said.

President Biden will return to America on Friday night. (BBC)

• President Biden, along with his son Hunter and sister, Valerie, viewing a plaque in honour of his late son, Beau