Prince Harry completed a charity fun run today wearing an usual item of kit - a Duke of Cambridge face mask.
The royal raced through the finish line with the paper image of his brother strapped to his face and surrounded by dozens of runners.
Harry had begun the event - a Sport Relief Mile race - close to Rio de Janeiro's Flamengo beach without the usual attire after setting hundreds of racers on their way by waving a Brazilian flag.
In the shadow of Rio's Sugar Loaf mountain the prince - dressed in sunglasses, polo shirt, trainers and track suit bottoms - joined them setting off at a slow jog and was joined by blind athlete Alice de Oliveura Correio, 17.
But he completed the mile long course in quick time - around six minutes - and as he saw the finish line in sight sped up.
Harry, 27, and William, 29, never miss an opportunity to continue their friendly rivalry whenever they are away on tour with the brothers usually poking fun at each other in speeches.
In an address to launch the Great campaign to promote Britain around the world earlier today the Duke's younger brother joked about his older sibling's dancing abilities.
He said: "But everything about Rio makes you want to dance. I'm just so thankful that my brother isn't here because he might actually do it... and that would not be cool."
Amanda Horton-Mastin from Sport Relief said: "It's wonderful that Harry is here in Brazil taking part in the Sport Relief Mile joining thousands of people who are doing a Mile around the world as well as the million people who will be doing it in the UK.
"It's great that this morning he's seeing how we raise the money and this afternoon he will see how the money is spent when he opens a project that Sport Relief is funding in the Alemao favela."
It appears the joke mask was a spur-of-the-moment jape - aimed at earning Harry bragging rights against his brother when he returns home next week.
Harry is thought to have been given the mask by another runner, one among hundreds of children and adults taking part in the event in temperatures well into the 90s.
William has got his own back on his brother in the past and usually makes reference to his red hair when on a foreign tour.
Harry was joined for part of the run by 17-year-old Alice de Oliveura Correio, a leading 200-metre runner and long-jump athlete.
She said: "To run with 'William' was fantastic, very cool."
Model Lily Cole, who attended the launch of the Great campaign earlier, also took part in the event but was wilting in the hot temperatures.
"It's been amazing running the Sport Relief Mile today but it's so much hotter than in my gym," she said.
The prince, who is in South America at the request of the Government, was taking part in a British-themed sports day - part of a Great campaign event to celebrate the passion Brazil and the UK share for sports, an organiser said.
Great aims to promote Britain in key foreign cities on the back of the Queen's Diamond Jubilee and London 2012 to encourage those overseas to visit, study or do business in the UK.
Harry's next event was touch rugby with some youngsters on the beach.
The prince was desperate to win, and as in his "race" against Usain Bolt in Jamaica, where he used a little subterfuge to claim victory, he grabbed the tops of the little boys as they tried to run past him.
At one point he picked up two boys and held them under his arms to allow a team mate to score.
The prince appeared to enjoy the action, and was seen knocking over two children - one from each side - in his bid to stop a try.
But he made amends by picking a little girl up.
Beach volley ball gave him the chance to show off his ball skills, and he wore a number 11 top in Brazilian colours for a three-a-side match.
The women players are known for their skimpy outfits, but they were modestly dressed in shorts and vest tops for the game.
On Harry's team was Brazilian Adriana Behar, one of the world's outstanding beach volleyball players of her generation.