Legendary broadcaster Sir Michael Parkinson has admitted that he was baffled by Ian Thorpe's decision to keep his homosexuality a secret.

Australian five-time Olympic swimming champion Thorpe revealed in an interview with Parkinson last July that he is gay.

"I said to him at the time, 'why the hell did you think that because you were gay that you had to keep it a secret? Who gives a toss?'" Parkinson told News.com.au.

"Why did he waste all that time feeling cut off? I think [the interview] purged him of a great feeling of guilt. It is an indication of how Australia has grown up - that he has been accepted."

In February last year, Thorpe spent some time in a rehab facility after he was spotted looking disoriented close to his parents' home in Sydney.