Sergio Motsoeneng, 21, was awarded pounds 600 for finishing ninth in last month's 90km race.
An investigation was launched after a runner fartherback in the field complained that Sergio had not overtaken him. But after examining time sheets and the results of the computer timing system, the race referees initially cleared him of cheating.
The brothers' plan was only foiled because photographs of the race published in Beeld, Johannesburg's daily newspaper, showed runner number 13018 at one stage wearing a yellow watch on his left wrist. At another stage the runner with that number was wearing a pink watch on his right wrist. Other photos later revealed Sergio twice swapping clothes with his 19- year-old brother, Arnold, in portable lavatories.
With evidence mounting against him, his lawyer advised him to own up to Cheryll Winn of the race's Jury of Appeal. Sergio has already made arrangements to return the trophy, but Ms Winn said: "Apparently he's already spent the money."Reuse content