On May 3, 1921, six counties on the island of Ireland became the legal entity known now as Northern Ireland.

The Government of Ireland Act 1920, whose long title was "An Act to provide for the better government of  Ireland," received its royal assent in December 1920 and came into effect just after midnight on May 3, 1921.

Also known as the Fourth Home Rule Bill, the Act established six counties on the north of the island of Ireland - Antrim, Armagh, Derry, Down, Fermanagh, and Tyrone - as the legal entity of Northern Ireland, a part of the United Kingdom.

The remaining provisions of the Act were repealed under the Good Friday Agreement in 1998.

In a statement published on May 2 to mark the centenary of Northern Ireland, Queen Elizabeth addressed the people of Northern Ireland and extended her "warmest good wishes."

She wrote: "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.

"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.

"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.

"I also wish to recognise the important contribution made by our friends and closest neighbours towards the success of Northern Ireland. 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."

The Queen has sent a message to the people of Northern Ireland on the centenary of the Government of Ireland Act coming into effect. pic.twitter.com/vMRmcxcR9K

— The Royal Family (@RoyalFamily) May 3, 2021

In his statement, UK Prime Minister Boris Johnson said that the centenary is "an important opportunity to come together to celebrate Northern Ireland and build towards a better and even brighter future for all of its people."

My message on Northern Ireland’s centenary year. pic.twitter.com/x5giX4bMwT

— Boris Johnson (@BorisJohnson) May 3, 2021

Brandon Lewis, the Secretary of State for Northern Ireland, said: “A hundred years on, and Northern Ireland’s Story is still in the making.”

WATCH: On the 100th anniversary of the Government of Ireland Act coming into effect, Secretary of State @brandonlewis says there is ‘much to be proud of in modern day Northern Ireland’ and reiterates the @NIOgov commitment to marking the Centenary in an inclusive way👇 pic.twitter.com/Tn9WbQmcbK

— Northern Ireland Office (@NIOgov) May 3, 2021

In March, the British government announced a series of events to mark the centenary of Northern Ireland.

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