Prime Minister Theresa May has said she will be "honoured" to join thousands of descendants of soldiers who fought at Passchendaele to commemorate the centenary of the First World War battle in Belgium on July 31.
Mrs May will break off from her three-week summer holiday to join the Prince of Wales and Duke and Duchess of Cambridge in paying their respects to those who fell in the Third Battle of Ypres, which began on July 31 1917 and lasted until November that year.
The commemorations will be preceded on the night before by the traditional Last Post ceremony, which has taken place every evening at the Menin Gate memorial in Ypres since 1928.
As part of the ceremony, representatives of combatant nations will lay wreaths under the Gate.
Descendants of those who fought in the battle were invited earlier this year to enter a ballot for 4,000 tickets to attend the commemoration event at the Commonwealth War Graves Commission's Tyne Cot Cemetery, where 11,961 men are buried.
Serving military personnel and descendants will read out letters and diaries from their ancestors as part of a service of remembrance.
Images from the war and recordings of interviews with First World War veterans will be projected onto the town's Cloth Hall.
Mrs May said: "The name Passchendaele resonates with anyone with even a passing knowledge of the First World War.
"It is on those fields where hundreds of thousands of men of all nations fought and died in appalling conditions.
"This event will be a fitting tribute not just to those men but also to the families and communities affected by their loss.
"I am honoured to be attending alongside the descendants of those who took part in the battle.
"The anniversary is a timely reminder of the horror of the First World War and the need for friends and allies to continue to work together in the pursuit of peace."
The battle for a number of ridges south and east of the Belgian town of Ypres lasted three months, one week and three days and resulted in massive loss of life on both sides, though exact numbers are disputed.
By the time British and Canadian forces finally took control of the tiny village of Passchendaele around a third of a million British and Allied soldiers had been killed or wounded in some of the most horrific trench warfare of the conflict.