The King also received a message of condolence from the Speaker of the Northern Ireland Assembly.

Sinn Féin's Alex Maskey said the Queen recognised how a "small but significant gesture can make a huge difference in changing attitudes".

The royal couple spent just over four hours in Northern Ireland.

Their first engagement was at Hillsborough Castle, the only royal residence in Northern Ireland, which has been a focal point for floral tributes to the late Queen.

The King and Camilla, the Queen Consort, met well-wishers in the County Down village, before the King held a private meeting with Northern Ireland Secretary Chris Heaton-Harris and senior representatives from Stormont's political parties.

The royal couple then travelled into Belfast for a service in St Anne's Cathedral, Belfast.

Irish address from speaker

Speaking at Hillsborough Castle, the King said the late Queen had seen momentous and historic changes throughout her long reign.

"My mother felt deeply, I know, the significance of the role she herself played in bringing together those who history had separated and extending a hand to make possible the healing of long-held hurts," he said.

"Now, with that shining example before me, and with God's help, I take up my new duties resolved to seek the welfare of all the inhabitants of Northern Ireland."

Starting his speech in Irish, Mr Maskey, Sinn Féin's longest-serving elected representative, said: "Ba mhaith liom comhbhrón a dhéanamh leat ag an am crua seo (I would like to sympathise with you at this difficult time).

"It's extraordinary to consider how much social and political change Queen Elizabeth witnessed... throughout her long reign.

"Yesterday an assembly of unionists, republicans, nationalists and those for whom the Constitution is not a main focus united to pay tribute to the late Queen.

"When she first came to the throne, no one would have anticipated an assembly so diverse and inclusive."

King Charles III and Camilla, the Queen Consort arrived at Belfast City Airport

After leaving Hillsborough Castle the royal couple travelled into Belfast to meet leaders from all the major faiths in Northern Ireland before a service of prayer and reflection on the life of Queen Elizabeth II at St Anne's Cathedral.

During the service, Archbishop of Armagh John McDowell, the head of the Church of Ireland, highlighted the Queen's efforts to foster peace on the island of Ireland.

He told the King and Queen Consort that "faithfulness, care, dutifulness, love and devotion" were all part of her long reign.

"All of these could be employed to describe her relationship with Northern Ireland, with patience binding them all together, but paying attention especially to what she said most recently, the word which I think will be most associated with Queen Elizabeth and Ireland, north and south, is 'reconciliation'," the archbishop said.

He added that the Queen "followed where Jesus led as women often have in the elusive and unfinished work of reconciliation here in Ireland".

Prime Minister Liz Truss attended the service, along with Irish President Michael D Higgins and Taoiseach (Irish Prime Minister) Micheál Martin.

Again, hundreds of people lined the route through the city.

The Reas from Carryduff and the Dolans from Belvoir took the day off school and made their way to City Hall at 08:00 BST to see the royal couple.

Back (LR) - Jack Rea, Nicola Rea, Lisa Dolan Front - Sophie Rea, Harry Dolan

"We'll never see anything like this again," said Lisa Dolan.

"It's a once in a lifetime event."

Ms Dolan said she felt sorry for the King being "unable to grieve the way the rest of us would", but understood it was his duty as monarch.

"He's been working towards this his entire life," she added.

Hazelwood Integrated students Jo and James were among those who gathered at Writers' Square, across from St Anne's Cathedral.

Hazelwood Integrated students Jo and James hoped to see the royal couple after the service at St Anne's Cathedral

They said that as history students, they were excited to be witnessing such an historical event.

"I was a wee bit heartbroken when the queen died - I'm not going to lie," said James.

But he was equally excited to see the new King.

"I had never really thought about the Queen as a force in my life until she died and then it felt like something was missing," Jo said.

Irish President Michael D Higgins greeting Prime Minister Liz Truss at St Anne's Cathedral

At the end of the service, the King and Queen Consort left St Anne's through the west door where they again met members of the public in Writers' Square, before heading back to Belfast City Airport for the return flight to London.