D-Day 80th anniversary: Emma Little Pengelly representing Northern Ireland at main commemoration in Portsmouth

The King addressing those gathered for the D-Day 80th anniversary commemoration in Portsmouth - BBC

In a video message ahead of the packed programme of events, which is being attended by the King and dignitaries from around the world, the deputy first minister said: "It is an incredible honour to represent Northern Ireland at the 80th anniversary D-Day commemorations.

"I'll be representing Northern Ireland, along with the first minister of Scotland, the first minister of Wales and the prime minister at the service in Portsmouth on 5 June, and in Normandy on 6 June.

"There were many, many tens of thousands of young men that fought in the World War. Many of those fought in Normandy and on D-Day. Many of those paid the ultimate sacrifice.

"But it was not just the over 60,000 young men of Northern Ireland, but many from across this island as well.

"It is a huge honour to be representing their sacrifice, and incredible service, for freedom, democracy and for our country."

Codenamed Operation Overlord, the allied invasion of mainland Europe on D-Day on June 6, 1944, was the greatest combined land, sea and air operation ever launched.

More than 150,000 British, American and Canadian troops landed on French beaches in an all-out effort to drive the Nazis out of France and the other occupied countries.

Emma Little Pengelly in Portsmouth for the D-Day anniversary commemorations

The tributes from Portsmouth – including military musicians and a flypast by the Red Arrows – are being broadcast live on BBC One and BBC iPlayer.

The event is being hosted by Dame Helen Mirren.

Addressing the invited guests from a specially constructed stage at Southsea, the King praised the commitment of everyone involved in the D-Day landings.

He said: “It is our privilege to hear their testimony, but our role is not purely passive. It is our duty to ensure that we, and future generations, do not forget their service, and their sacrifice, in replacing tyranny with freedom”.

D-Day veteran Roy Hayward at Portsmouth - BBC

In his programme notes for the event, the King spoke of his “profound admiration and respect” for those who took part in D-Day, adding: “It remains our solemn duty to continue to honour the outstanding gallantry, service and sacrifice of those who took part in that perilous mission.”

At the Portsmouth commemorations, William read an extract from the diary of Captain Alastair Bannerman of the Royal Warwickshire Regiment, a soldier who was part of D-Day, addressed to his wife on the morning of the landings.

On Wednesday evening, A Tribute to the Fallen will include a community vigil to fallen Allied soldiers, including a live broadcast from Bayeux War Cemetery in France, hosted by Kirsty Young on BBC One.