For years, it's been one of the biggest questions in sport: did cyclist Lance Armstrong, the seven-time winner of the Tour de France, dope?
Lance Armstrong has denied wrongdoing but now a former teammate and roommate of Armstrong's, Tyler Hamilton, has produced the most detailed and wounding set of allegations yet.
Tyler Hamilton tells Tim Franks about the "dark era of cycling" and his hope that transparency about the past will make for a cleaner sport in the future.
You can watch the full interview on BBC World News on Tuesday 11th September 2012 at 03:30, 08:30, 15:30 and 20:30 GMT. It also broadcasts on the BBC News Channel in the UK at 04:30 BST on Tuesday 11th September and 00:30 BST on Wednesday 12th September 2012.
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