The Duke and Duchess of Cambridge will join Prime Minister Theresa May in Belgium later to mark the centenary of the Battle of Passchendaele – one of the bloodiest of World War One.
Half a million Allied and German soldiers were killed, wounded or went missing in action.
The ceremony will be held in the town of Ypres.
The King of Belgium and Prince William will lay wreaths at the Menin gate.
They will hear the Last Post, which has been played at the gate by a bugler almost every evening since 1928.
Dignitaries and the descendants of those who died will gather in Ypres’s Market Square for an event to tell the story of the battle.
Performances and music – which will include the National Youth Choir of Scotland, Dame Helen Mirren and a specially written extract from War Horse narrated by Michael Morpurgo – will be set to a backdrop of light projections on to the historic Cloth Hall.
Officially known as the Third Battle of Ypres, Passchendaele was fought from 31 July to 6 November 1917 in the West Flanders region of northern Belgium.
About 275,000 Allied troops and 220,000 Germans died in the battle.
British troops sought to push back the Germans from a ridge, near the Belgian town of Ypres during the three-and-a half month campaign, which is believed to have won the allied forces only small gains.
On Monday, the anniversary of the start of the battle, commemorations will continue with a special service held at Tyne Cot cemetery in Belgium, where thousands are buried and commemorated.