Thousands of people, including members of the Royal Family, have attended a ceremony in France to mark the centenary of the Battle of the Somme.
The Duke and Duchess of Cambridge and Prince Harry attended a vigil at the Thiepval Memorial on Thursday evening.
Prince William spoke of European governments “including our own” who failed to “prevent the catastrophe of world war”.
“We lost the flower of a generation; and in the years to come it sometimes seemed that with them a sense of vital optimism had disappeared forever from British life,” he said.
“It was in many ways the saddest day in the long story of our nation.”
At the Westminster Abbey service on Thursday, the Queen was joined by the Duke of Edinburgh as she laid flowers at the Grave of the Unknown Warrior.