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Prince William made an appearance in Brazil Saturday -- in spirit, at least.

Prince Harry donned a mask with his older brother's likeness during a mile-long Sport Relief run. "He thought it would be a bit of fun and give his brother a laugh. He hadn't planned to wear the mask but had spotted it on another runner and borrowed it," a royal aide told The Daily Mail. "It took everyone by surprise but he thought it was a real hoot and would make his brother laugh."

(William, 29, began his six-week tour of duty in The Falklands on February 1; wife Kate Middleton, 30, helped Queen Elizabeth kick off the Diamond Jubilee tour at St. Pancras train station in London Thursday.)

Royal redhead Harry, 27, ran alongside supermodel Lily Cole, chef Marcus Wareing and blind athlete Alice de Oliveura Correio, 17.

The prince and his Scotland Yard police protection team completed the race in 8 minutes, 32 seconds.

"To run with 'William' was fantastic, very cool," said de Oliveura Correio, a leading 200-meter runner and long-jump athlete.