Prince Harry, Prince William and Kate Middleton cheer on London Marathon runners

Run for a cause! Prince Harry, Prince William and Kate Middleton were filled with joy as they attended the Virgin Money London Marathon on Sunday. The royal trio was casually dressed in matching black ensembles that featured the logo of their mental health campaign Heads Together. They offered words of encouragement to the 700-plus Heads Together runners who were set to take part in the 26.3 mile race, which saw over 39,000 runners competing in total. Heads Together was chosen as the official charity for the 2017 London Marathon.

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Prince Harry, Prince William and Kate with London Marathon runners Photo: Getty Images

Before the race began, the Duke and Duchess of Cambridge and Prince Harry met a collection of runners, wishing them good luck and thanking some of them for supporting Heads Together. Then the royal three parked themselves at the start line where they pressed a large red button together, marking the beginning of the famous marathon. Later, William, 34, and Kate, 35, seemed to be having a wonderful time as they cheered and used small red horns to encourage the athletes along the way. Kate, in particular, was spotted giddily using the air horn. Then William turned the tables on her, jokingly pointing the horn at his wife in a cute and playful moment. The duo was also seen dutifully holding out water bottles for marathon participants to grab as they whizzed by.

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William jokes around with Kate Photo: Getty Images

As the charity runners powered through the finish line, William, Kate and Harry were there to conratulate them and hand out medals. The athletes were thrilled to have the family place medals around their necks. In a fun moment, Kate put a medal over a runner who was dressed as a giant white star. Meanwhile, Prince Harry, 32, who is patron of the London Marathon Charitable Trust, got ready to make the official presentations to winners of the elite men, women, and wheelchair races.

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Kate hands out medals to the runners Photo: Getty Images

In the build up to this year’s marathon, William, Harry and Kate have made several public appearances to discuss the important work of heads together as well as some personal revelations. It began when Harry opened up about seeking therapy to cope with his ongoing grief of the death of his mother Princess Diana. Both brothers have spoken honestly about how their mother’s death affected them at such a young age and shaped who they are. In a film, which is part of the Heads Together campaign's #OkToSay series for the London Marathon, William and Harry discuss how the death of their mother brought them closer together.

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Prince William places a medal on a runner Photo: Getty Images

In the film, Harry said: "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 12, while William was 15, when their mother passed away during a tragic car accident in Paris in 1997.

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The royals are satisfied with their recent contribution to the rise of mental health awareness. Their spokesman released a statement saying, “The Duke and Duchess of Cambridge and Prince Harry have been overwhelmed by the response to the Heads Together campaign. We are in the middle of a truly national conversation on mental health. They are incredibly grateful to everyone who has shared their stories in recent weeks. And having asked others to start conversations on mental health with their friends and families, they wanted to show that they are taking part as well. They hope the film shows how positive a conversation on mental health can be.”