Athletics golden girl Cathy Freeman has told in her autobiography of the turmoil she felt when she told her estranged husband she was seeing another man.

Excerpts from Cathy: Her Own Story, serialised in the Sunday Telegraph, describe in Ms Freeman's own words the moment she revealed the affair with Australian actor Joel Edgerton.

Ms Freeman, the 400m gold medallist at the Sydney Olympics in 2000, told husband, Nike executive and cancer survivor Alexander 'Sandy' Bodecker, their marriage was over during a flying visit to Portland in the United States.

"I had decided there were three things I had to tell Alexander: One, I was seeing Joel. Two, the divorce was definitely happening. Three, I still wanted to be in his life," Ms Freeman wrote.

She described the moment she finally revealed the truth to her husband as they walked by a river.

"Lighting the cauldron at the Sydney Games was a breeze compared with the anxiety that was pulsing through my veins as I listened to Alexander talk," she wrote.

"I'm seeing someone," Ms Freeman wrote of her conversation with Mr Bodecker that day.

"It's Joel Edgerton."

Ms Freeman also admits: "I had to tell Alexander about Joel ... because everyone knew except him."

After the talk, Ms Freeman said she told her husband she needed to go to the bathroom but rang Mr Edgerton instead.

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