King Charles and the Prince of Wales joined world leaders and veterans at a series of events to mark the 80th anniversary of the D-Day landings.
Both royals made speeches in France on Thursday, praising the "bravery and sacrifice" of those who "served at that critical time".
The King laid a wreath at the British Normandy Memorial in Ver-sur-Mer, near Gold Beach, with a note attached touching on the sacrifices made on D-Day.
Later in the day, Prince William joined heads of state at Omaha Beach in Saint-Laurent-sur-Mer for the final event of the two-day commemorations.
In a speech at the British war memorial in France, the King said the lesson to learn was that free nations must stand together to oppose tyranny.
"Our obligation to remember them, what they stood for, and what they achieved for us all, can never diminish," the King told the delegation at a sombre and emotional commemoration.
UK Prime Minister Rishi Sunak and Labour leader Keir Starmer attended the same ceremony as the King, in what may be one of few remaining anniversaries that D-Day veterans will attend.
On 6 June 1944, tens of thousands of soldiers landed on five beaches in Normandy in northern France.
The landings were the start of the campaign to liberate Nazi-occupied north-western Europe.
Five years ago, 225 British veterans travelled to Normandy for commemorations. This year, there were 23, including some centenarians.
One US Navy veteran travelling to France, Robert "Al" Persichitti from Rochester, New York, died on his way to the event, a veteran organisation has confirmed.
He was airlifted to a hospital in Germany on 30 May after suffering a medical emergency aboard a ship heading to Europe. He died the following day, aged 102.
Thursday's commemorations began early in the day with a military piper at Gold Beach in Arromanches, who played a lament at sea at 07:26, marking the exact moment when the invasion began.
That heralded a series of re-enactments, military flyovers and memorial services in several locations.
Those present at Thursday's events also included US President Joe Biden and Canadian Prime Minister Justin Trudeau - the leaders of the other main powers involved in the landings.
Prince William was at the Canadian commemorative ceremony at Juno Beach, where he thanked Canadian veterans for their "extraordinary acts of bravery and sacrifice".
"We continue to honour every Canadian, who gave so much, every Canadian family who lost a loved one," he said.
He ended his speech by saying in French: "Thank you for our freedom, and thank you for your service."
Mr Trudeau also paid tribute, saying: "We must all continue to stand for democracy day in day out, we owe it for future generations."
Prince William sat alongside world leaders at the final event of the commemorations, the international memorial ceremony at Omaha Beach.
William spoke to President Biden, French President Emmanuel Macron and Ukrainian President Volodymyr Zelensky ahead of the event.
Mr Sunak did not attend the Omaha Beach ceremony, but UK Foreign Secretary David Cameron and Mr Starmer were both present.
During the event, President Biden said that what happened 80 years ago in Normandy did not absolve modern generations from doing what had to be done today.
"Democracy is never guaranteed," he said. It had to be preserved and fought for, he added.
Mr Biden said the struggle of Ukrainians in the face of Russian aggression captured the spirit of D-Day.
He described the conflict as being part of an unending struggle between dictatorship and freedom.
'Heroes in the shadows'
At the Gold Beach ceremony, President Macron honoured the bravery and sacrifice of those who fought.
"France will never forget the British troops who landed on D-Day and all their brothers-in-arms," he said.
"That faith in freedom which you have never lost, that constant selflessness and devotion both guide us and serve as a duty to us."
Mr Macron awarded Légion d'Honneur medals to veterans including Christian Lamb, now 103, who spent the war as an officer in the Women's Royal Naval Service.
In 1944, she helped plan the D-Day landings from Churchill's secret war rooms in London.
"You were one of the heroes in the shadows," the French president told her.
Other veterans present included 99-year-old Joe Mines, who landed on Gold Beach 80 years ago.
In words read by actor Martin Freeman, Mr Mines said he had come back "to pay my respect to those who didn't make it".
Roy Hayward, now 99, took part in the landings as a trooper in the Sherwood Rangers and was badly wounded in the assault.
"The tank was hit and I was so badly damaged they had to amputate both legs below the knee," he told the BBC. "I always consider myself one of the lucky ones that survived, because so many of us didn’t."
Also taking part in the day of tributes were President Volodymyr Zelensky of Ukraine, and German Chancellor Olaf Scholz. No Russian official was invited.
Meanwhile, American actor Tom Hanks and film director Steven Spielberg joined the commemorations in Normandy.
Their 1998 film Saving Private Ryan depicted the US landings on Omaha Beach in its famed opening battle scene.
The film is being shown in around 300 French cinemas on Thursday to mark D-Day.