Northern Ireland First Minister Peter Robinson joined world leaders in France yesterday to pay tribute to the men who took part in the D-Day landings.
Her Majesty the Queen, US President Barack Obama, French President Francois Hollande and Russian President Vladimir Putin were among those who travelled to France for ceremonies.
Hundreds of Second World War veterans were also present to mark the 70th anniversary of the landings in Normandy which marked a major breakthrough in the conflict.
On June 6, 1944, 156,000 British, US and Canadian forces invaded the coast of northern France.
As many as 4,000 Allied troops and 9,000 German soldiers died in one day.
The Queen paid her own tribute to those who made the ultimate sacrifice for freedom in Europe, laying a wreath in a military grave, the last resting place of many British D-Day troops.
She left her floral tribute during a solemn open air ceremony at the Commonwealth War Graves Commission cemetery in Bayeux, the first town to be liberated following the Normandy landings.
Prince Charles also laid a wreath, as did Prime Minister David Cameron and other world leaders.
The ceremony took place on the French northern coast at Sword beach, the codename for one of the Allies' five landing points where, following a speech from Mr Hollande, scenes from the invasion were re-enacted.
The Queen spoke of her pride "in the men who stormed those beaches" and "thankfulness knowing that today our nations are free and sovereign" because of allied efforts.
She added that the UK and France were "joined together by the common experience of struggle, sacrifice and reconciliation".
Mr Cameron, who was in Normandy along with Nick Clegg, Ed Miliband and Scotland's First Minister Alex Salmond, said he felt a mixture of "awe and gratitude" after meeting veterans.
"I think the clear evidence of what happened in 1944 and 1945 is the importance of standing up together for freedom and security," he said.
Mr Robinson attended a service at the Bayeux Cathedral, Bayeux Cemetery and an international ceremony at Sword beach.
He said he was deeply honoured to be there for the 70th anniversary of the Allied invasion of Nazi-occupied Europe.
"We must never forget the bravery, courage and sacrifice of those thousands of soldiers who fought and for the many who ultimately gave their lives for all of us," he said.
"It is right that those veterans are central to today's commemorations.
"Northern Ireland provided a staging platform for allied forces prior to the D-Day landings."
He added: "We are all eternally grateful to the men and women of Northern Ireland who played their part in one of the most significant engagements in military history."
The poignant anniversary was also marked with a number of events on the other side of the English channel.
In Arromanches, the Duke and Duchess of Cambridge applauded as veterans paraded in front of them yards from Gold beach in a Normandy Veterans' Association service.
Some 156,000 Allied troops landed on the five invasion beaches on June 6, 1944, in an operation which wartime Prime Minister Winston Churchill described as: "Undoubtedly the most complicated and difficult that has ever taken place." It marked the beginning of an 80-day campaign to liberate Normandy which involved three million troops and cost the lives of 250,000 people.