The Duchess of Cambridge was greeted next to the Weeping Window sculpture by Diane Lees, director general of Imperial War Museums (Picture: PA).
The Duchess of Cambridge has heard the "sad stories" of three brothers from her family who were killed fighting during the First World War.
Kate was shown for the first time the original documents detailing the lives and deaths of the Lupton brothers - Francis, Maurice and Lionel - killed in France, including a postcard sent on the day one died.
The men were the siblings of Olive Middleton, Kate's great-grandmother, who worked as a nurse with the Voluntary Aid Detachment during the war, and was married to Richard Middleton.
When shown an official letter from Buckingham Palace conveying the sympathy of King George V after the third brother had died, the duchess said:
"I'm sure so many families had this type of letter and sad stories."
She also reacted to the brief telegram sent by her great-grandfather Richard Middleton, an Army officer, who wrote to his father-in-law saying Francis' body had been found after he was killed instantaneously by a bomb during the Battle of the Somme.
Kate said: "It's so bland, hardly any words."
The family papers were donated by one of Kate's distant relatives around a month ago and now form part of the Imperial War Museums' documents archive.
The Duchess toured the popular visitor attraction, which was full of school groups and parents with their children to see the documents and visit the First World War Galleries.
Earlier this month, a giant poppy display commemorating the First World War, known as the 'Weeping Window' arrived at the final stop of its four-year nationwide tour.
The sculpture features ceramic poppies streaming out of an upper window of London's Imperial War Museum.