After years of dismissing speculation about his sexuality, Ian Thorpe has revealed he is gay.

Thorpe made the admission in a tell-all interview with Sir Michael Parkinson, News Corp reports.

The interview, which will air on Sunday night on Channel Ten, has been described by Sir Michael as one he had wanted to do for a long time.

“Ian Thorpe has always been near the top of my list to interview. The reasons are obvious. Not many athletes can claim to be the best of all time. Ian can."

Before he retired for the first time at the age of 24, Thorpe broke 22 world records and won five gold and three silver medals and one bronze medal at the Olympic Games.

But despite his success in the pool, Thorpe's career has been plagued with persistent rumours about his sexuality.

In his 2012 autobiography, This is Me, Thorpe confronted the speculation 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.''

Earlier this year, Thorpe was admitted to a rehabilitation facility to receive treatment for his ongoing battle with depression.

He discussed his battle with the illness in his autobiography, revealing that at times it had become so severe that he had considered suicide and had planned specific places and ways to kill himself.