The Queen has said that the peace in Northern Ireland is a "credit to its people" as she marked the centenary of the creation of the province, but warned that reconciliation cannot be taken for granted.
In a warm personal message, Her Majesty, 95, recalled with "fondness" her visit to Ireland with the Duke of Edinburgh ten years ago this month, revealing that she treasures the memories and the spirit of goodwill they witnessed.
She said the peace process was a credit to the leaders who had the "vision and courage to put reconciliation before division" but that the continued peace was "a credit to its people, upon whose shoulders the future rests."
The Government of Ireland Act came into force on May 3, 1921, formalising the partition of the island and retaining six counties of the ancient province of Ulster within the UK.
The anniversary comes at a turbulent time, following the resignation last week of Arlene Foster, the leader of the Democratic Unionist Party and the province's first minister, which alongside Brexit and Nicola Sturgeon’s demands for a second independence referendum in Scotland, has prompted renewed questions about its governance and borders.
The province is also reeling from recent rioting in Loyalist areas and mounting anger over the complex Northern Ireland Protocol.
The Queen said the anniversary served as a reminder of the UK and Ireland’s "complex history" and provided an opportunity to "reflect on our togetherness and our diversity."
"In Northern Ireland today, there is, perhaps more than ever, a rich mix of identities, backgrounds and aspirations, and an outward-looking and optimistic mindset," she said.
"The political progress in Northern Ireland and the peace process is rightly credited to a generation of leaders who had the vision and courage to put reconciliation before division.
"But above all, the continued peace is a credit to its people, upon whose shoulders the future rests."
Her Majesty added: "It is clear that reconciliation, equality and mutual understanding cannot be taken for granted, and will require sustained fortitude and commitment.
"During my many visits to Northern Ireland, I have seen these qualities in abundance, and look forward to seeing them again on future occasions."
The Queen said she wanted to recognise the "important contribution made by our friends and closest neighbours towards the success of Northern Ireland."
She added: "I look back with fondness on the visit Prince Philip and I paid to Ireland, ten years ago this month. I treasure my many memories, and the spirit of goodwill I saw at first hand.
"Across generations, the people of Northern Ireland are choosing to build an inclusive, prosperous, and hopeful society, strengthened by the gains of the peace process. May this be our guiding thread in the coming years.
"I send my warmest good wishes to the people of Northern Ireland."
It was signed "Elizabeth R".
Meanwhile, Boris Johnson said the UK Government would continue to showcase "all the brilliant things" that Northern Ireland contributes to the rest of the UK in a message to the country to mark its centenary.
The Prime Minister said on Twitter: "This is a very significant national anniversary, marking the 100th year since the Government of Ireland Act came into effect and the formation of the United Kingdom as we know it today.
"Throughout 2021, in its centenary year, the Government will continue to showcase all the brilliant things Northern Ireland contributes to the rest of the UK and the world, from its world-class fintech industry and research capabilities, to its inspiring young people, and its vibrant culture of arts and sport.
"It is also important that we pause to reflect on the complex history of the last 100 years. People from all parts of Northern Ireland, the Republic of Ireland, the United Kingdom and across the globe, will approach this anniversary in different ways, with differing perspectives.
"While this is a moment of shared reflection, it is also an important opportunity to come together to celebrate Northern Ireland and build towards a better and even brighter future for all its people."