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Prince William, Prince Harry and Kate cheer on runners at the London Marathon

Sophie Hamilton

Prince William, Prince Harry and Kate were all smiles as they attended the Virgin Money London Marathon on Sunday. The royal trio were dressed casually in trousers and matching black tops which featured the logo of Heads Together – the mental health charity which they are supporting for the marathon. Over 700 Heads Together runners are set to take part in the 26.3 mile race, with more than 39,000 runners competing overall.

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Princes William, Prince Harry and Kate at this year's London Marathon

The Duke and Duchess and Prince Harry were pictured pressing the button to begin the famous marathon. They also met some of the runners personally before the race and then cheered them on from the side-lines. William and Kate looked to be having a wonderful time as they tooted their small red horns to encourage runners along the way. The royal couple are due to hand out medals to some of the charity runners when they cross the finish line later in the day. Prince Harry, who is patron of the London Marathon Charitable Trust, is set to make the official presentations to winners of the elite men, women, and wheelchair races.

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The Duke and Duchess of Cambridge cheering on the runners 

In the build up to this year’s marathon, William, Harry and Kate have made several public appearances to discuss the work of charity Heads Together. Both Harry and William have spoken openly about how their own mother’s death affected them at a young age. In a film as part of the Heads Together campaign's #OkToSay series for the London Marathon, the footage sees the brothers reveal how the death of their mother, Princess Diana, had brought them closer together.

READ: Kate reveals she and Prince William struggled after Prince George's birth

Harry revealed in the film: "Both of us have always been open to each other, but we've never really talked about it. We've never really talked about losing a mum at such a young age." He added: "You then when you speak to other people's families and little kids, you think 'wow I don't want them to have to go through the same things'. You want to with a little bit of experience, you want to help as much as you can and try to empower them to have that conversation. You want it to be brave for themselves to talk about it at a young age rather than bottling it up for far too long." Prince Harry was just 12, while William, 35, was 15 when their mother died in a tragic road accident in Paris in 1997.