Ian Thorpe, who won five Olympic gold medals and set numerous world records during his swimming career, suddenly quit in 2006 saying he no longer enjoyed it and was fed up with the media intrusion into his private life.
Now he is swimming again and for the first time reveals how a "crippling depression" affected him, even at the peak of his career.
He tells HARDtalk's Stephen Sackur about having suicidal thoughts, drinking too much and how he hid his despair from those closest to him.
You can watch the full interview on BBC World News on Monday 12 November at 15:30 and 21:30 GMT and on Tuesday 13 November at 04:30, 09:30, 15:30 and 21:30 GMT.
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