Prince Harry sprinted past his brother and sister-in-law during a relay race at a training session for runners taking part in the London Marathon.

The royal trio laced-up their trainers and took to the track at the Queen Elizabeth Olympic Park in east London for their mental health campaign Head Together.

Joined by around 150 runners, William, Kate and Harry competed against one-another for the 50 metre sprint. Kate, who wore a red puffer jacket and black jeans, tied back her hair on the start line alongside her husband.

William joked, "Oh my hamstring" after being briefed before the race.

Despite an impressive sprint, the Duchess was beaten by both William and Harry - who were wearing chinos and trainers.

At one point, the Duke crossed into the Duchess's lane. William and Kate are known for their competitive nature but the couple laughed and hugged on the finish line, while Harry patted his brother on the back.

Each royal ran with the relay with a team of runners including athletes Iwan Thomas and Paula Radcliffe and presenter Sian Williams.

The training day was organised for runners taking part in the marathon for Heads Together - an umbrella organisation spearheaded by the three royals.

It aims to change the national conversation on mental well-being to a positive one, and is a partnership between eight charities that provide front-line mental health support.

The organisation is the charity of the year for the 2017 London Marathon, and Heads Together says it wants to use this privileged position to further tackle the stigma surrounding mental health.

In a speech to the runners at the Copper Box Arena at the Olympic Park, William said it had fallen to him as "the only elite athlete runner between the three of us to say a few words".

The 34-year-old wished the marathon runners good luck and said: "We want to normalise mental health, we want to get people talking about it to make it more normal, to reduce the stigma and by what you guys are doing and having so many of you here today we've already seen the benefit of joining in by being a part of this marathon.

"We want to make it the mental health marathon so that we can get more people talking and break down the stigma."

Marathon world record holder Paula Radcliffe gave advice to the Heads Together athletes at the training day and said it was "really great" that the royals had got behind the charity.

She said Kate, in whose team she competed in the relay, told her that she loves running daily.

"We were chatting afterwards and she said she was more of a sprinter, which was good for the relay, but she really enjoys being able to get out and run every day - I don't know if she runs every day now but she did used to at university and she certainly runs quite a bit," Radcliffe told the Press Association.

But the athlete said William's claim that he was an "elite athlete" was stretched.

"I think he was ad-libbing a little bit.

"He was saying that when they started the race they thought they were going to do an easy run through, and then the other two decided to spring a bit of a competitive sprint on him, but he was able to reel them in quite quickly.

"I'm going to teach him to stay in his lane though because I'm sure he should be disqualified for that."

Radcliffe, who described the London Marathon as her favourite race, added that it would be "really great" to get William, Kate or Harry to run the 26.2 mile race, but said security issues, "rather than a lack of willingness on their behalf", prevented them from doing so.