The royals will commemorate the 200th anniversary of the Battle of Waterloo.
Britain's Queen Elizabeth II
According to the Daily Express newspaper, the family will play a key role in remembering those who fell on both sides during the conflict in 1815.
They will be joined by heads of Government and ambassadors at the service at St Paul's cathedral on June 18, as well as at least 200 descendants of those who fought in the battle between the French and Anglo-allied armies which took place just outside of Brussels.
Is is thought that a member of the royal family will also be taking part in a dramatic reenactment of the moment Major Henry Percy arrived in London on June 21 carrying two French eagle standards and marched up the steps at the Boehm family residence near Pall Mall to inform the Prince Regent, George IV, of the Duke of Wellington's victory over Napoleon.
An actor - who is yet to be named - will play the part of Major Henry Percy.
The commemoration is being organised by Waterloo 200 in order to raise awareness of the battle's historical significance to the public, especially schoolchildren.
The organisation has also put on a 200 object exhibition - which includes photographs of Wellington and false teeth - to show the history of the campaign, on their website.
Waterloo 200's Chairman, Major General Sir Evelyn Webb-Carter said: "This is about trying to educate the young and anyone who is interested about why this anniversary is so important.
"The Battle of Waterloo brought an end to a very long war which had run for 22 years and was known at the time as the Great War.
"It heralded the start of a much more stable Europe and set in train the building of the nation states of Europe which we know now.
"The battle was a full stop in European history."