King Charles has paid a heartfelt tribute to those who took part in the D-Day landings, praising them for “replacing tyranny with freedom”.
“We are eternally in their debt,” the King told a commemoration on the eve of Thursday’s 80th anniversary.
He was speaking in Portsmouth, one of the key departure points for the Normandy landings in June 1944.
The King hailed the “courage, resilience and solidarity” of those who had taken part in D-Day and whose numbers were now “dwindling to so few”.
Wednesday was the first of two days of commemorative events taking place in both Britain and France.
On Wednesday evening, crowds watched a spectacular drone light show in Portsmouth.
At the same time, on the other side of the Channel, thousands of headstones were illuminated in honour of fallen Allied troops at the Bayeux War Cemetery.
Earlier in the day, crowds gathered near Sannerville, Normandy, to watch a large-scale parachute re-enactment of the Allied liberation of the region.
King Charles, with Queen Camilla and his son the Prince of Wales, addressed a national D-Day commemoration held under blue skies on Southsea Common on Wednesday morning.
The audience rose to their feet when veterans stood to make speeches and the Queen was brought to tears.
In his biggest public speech since his cancer diagnosis, King Charles hailed the “greatest amphibious operation in history” and the courage of those who “must have questioned if they would survive”.
The King said their efforts to end “brutal totalitarianism” must never be forgotten.
And he called on the present generation to honour those who had died, in ways that “live up to the freedom they died for, by balancing rights with civic responsibilities”.
Prince William delivered a poignant reading from the diary of Captain Alastair Bannerman, in which the soldier remembered his family as he headed towards the French coast on the morning of D-Day. Captain Bannerman survived the landing and the war, Prince William said, adding: “Too many never returned.”
Speaking to some of the veterans later, Prince William was asked about his wife Catherine’s recovery and said: “She’d love to be here today.”
He said Catherine’s grandmother had worked at Bletchley Park, the top-secret home of the World War Two codebreakers, and “never spoke about anything until the very end” of the war.
“It was all very secret,” he added.
Dame Helen Mirren praised the bravery of the veterans in attendance during her introduction to the event at 11:00 BST, while Prime Minister Rishi Sunak read an address to the crowds.
Portsmouth was one of the embarkation points on the south coast eight decades ago, as Allied forces crossed the Channel to liberate France and Western Europe from Nazi occupation.
Foundations for the Allied victory were laid by the success of the Normandy landings, in which troops from the UK, US, Canada and France conducted the largest seaborne invasion in history.
The commemorative event heard from those who took part in D-Day, including Roy Hayward, who landed in Normandy on 6 June 1944 at the age of 19.
Mr Hayward, now aged 98, said he wanted to remember those who had “fought for democracy” and “to ensure their story is never forgotten”.