Thorpe took to Twitter after the interview with Sir Michael Parkinson on Australia's Channel 10 aired, and expressed his gratitude for the messages of support he had received.
"I've thought about this for a long time. I'm not straight," said a tearful Thorpe in the programme.
"And this is only something that very recently, we're talking the past two weeks, I've been comfortable telling the closest people around me, exactly that."
[TWEET: Brett Lee - 'I'm really glad for Ian Thorpe. It doesn't matter as long as you're happy in your own skin. Well done, mate.']
"I've wanted to (come out) for some time but I couldn't, I didn't feel as though I could," he added.
"What happened was I felt the lie had become so big that I didn't want people to question my integrity.
"The problem was I was asked at such a young age about my sexuality. I went to an all-boys school... so if you're accused of being gay, the first answer is no and you get ready for a fight."
Homophobic taunts by members of the public had also not helped, but he admitted a big part of his reticence was that he worried that being gay would not fit into his image as "Australia's champion".
"Now it'll be something that I work on with a doctor," he said.
"I was already living somewhat of a lie in my life because I was trying to be what I thought was the right athlete by other people's standards.
"I wanted to make my family proud, I wanted to make my nation proud. Part of me didn't know if Australia wanted its champion to be gay.
"People will criticise me, some people won't like the idea other people may applaud me for it, but it's me."
[TWEET: Van den Hoogenband - 'You've always been a great champion, now even more! I'm proud of you.']
Parkinson himself said of the interview with the five-time Olympic champion: “I think his sexuality is no one’s business but his own. But I think it’s one of the best interviews I have ever done in terms of (Thorpe) talking about depression and things like that.”
Thorpe’s sexuality has been a persistent talking point throughout his remarkable career.
In his 2012 autobiography, This Is Me, Thorpe addressed the matter head on: ''For the record, I am not gay and all my sexual experiences have been straight.
“I'm attracted to women, I love children and aspire to have a family one day … I know what it's like to grow up and be told what your sexuality is, then realising that it's not the full reality. I was accused of being gay before I knew who I was.''
In February, Thorpe's manager confirmed the Australian hero had been admitted to rehab after suffering from depression.
Police were called after Thorpe was found disorientated and behaving oddly and the 31-year-old was taken to hospital.
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