Swimming legend Ian Thorpe admits he is a nerdy bookworm who hardly fits the stereotype of an Australian sportsman, but says rumors he is gay are not true.

Launching his autobiography This is Me on Wednesday, the five-time Olympic gold medalist opened up about his battle with depression and his failure to qualify for the London Games in his much-anticipated comeback.

"This is a very different book than I intended," said Thorpe, now 30, adding it was supposed to be the story of someone who got back in the pool and achieved "the success he had in the past".