tower london poppie kate middleton
Kate Middleton, Prince William and Prince Harry visit the Tower of London's "Blood Swept Lands and Seas of Red" ceramic poppy installation, commemorating the 100th anniversary of the outbreak of World War OneGetty

Prince Harry and Prince William paid a surprise visit to athletes in training for next month's Invictus Games at Lee Valley.

Inspired by the Warrior Games, in which wounded servicemen from the U.S navy, air force and army compete in a variety of track and field sports, the first British version will see more than 400 competitors from 14 different countries go head-to-head in venues across London.

Harry has been promoting the Games for the past few months and in a recent interview on Radio 2 spoke of his pride in being involved in the event.

Gold, silver and bronze medals have been created especially for the event by jewellers Garrard.

The Games will feature a celebrity-studded closing ceremony with a concert headlined by the Foo Fighters and the Kaiser Chiefs.

The Duke of Cambridge and Prince Harry have spent the week highlighting the work of other military charities, including Help for Heroes and the Royal British Legion.

During a visit to the Tower of London on Tuesday morning, both planted ceramic poppies in the moat for the installation Blood Swept Lands and Seas of Red, which will eventually include 888,246 flowers - one for every British and Commonwealth soldier killed in World War One.

Once the exhibition comes to an end on the 11th November, the poppies will be sold for £25 each, with proceeds going to military charities

The Invictus Games opens on the 10th September.