Five-time Olympic champion Ian Thorpe has denied using performance-enhancing drugs and promised to clear his name.
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."
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
"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.
"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."