Thorpe in the crowd at the World Championships in Melbourne

The French newspaper L'Equipe revealed that a test before Thorpe's retirement showed unusually high levels of naturally-occurring hormones.

"I have never cheated," said Thorpe, who admitted the existence of the test. "I was in complete shock to hear of this report, I didn't know what to do.

"My accomplishments in this sport in people's eyes are being diminished."

News conference: Ian Thorpe

Thorpe continued: "I had no previous knowledge of any result of this kind and I did not understand how a test result that supposedly related to me, which must have been undertaken some time ago given my retirement, could be being leaked to a French newspaper when I did not know about it.

I have complete confidence that all the evidence will establish that I am clean Ian Thorpe

"I can now confirm that a test that was undertaken in May 2006 while I was in Australia returned unusual levels of testosterone and a hormone called leutenising hormone. Both these substances are naturally occurring substances.

"There are many innocent physiological and pathological reasons why a test may return unusual levels of these substances.

"The Australian Sport Anti-Doping Authority (ASADA) were at pains to reassure me that I have not failed a drug test and they made it clear to me that any suggestion that is being made to this effect is just plain wrong.

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"I have complete confidence that all the medical and scientific evidence will establish that I am clean.

"I have always been, and remain, a strong supporter of the drug testing system. Most people will probably recognise that I have been one of the most tested athletes.

"My reputation as a fair competitor is the most valuable thing that I take out of my time in swimming."