Now, with the publication of her biography, she reveals the one secret she kept close: that she was born after her biological mother was the victim of date rape.

Yesterday, Beachley was at Wollongong's Dymocks bookshop signing copies of the book, Beneath the Waves, for which author Michael Gordon was given access to her family, friends and even her diaries.

Gordon is also the author of the Paul Keating biography, A Question of Leadership, so Beachley felt in safe hands, but she told the Mercury that finally reading a copy was a "heartbreaking" experience.

"I realised that I did just write it for myself," Beachley said.

"It was so cathartic and cleansing to put my whole life down on paper and then to reflect on it and be proud of it.

"My mother's stories were quite eye-opening, and then the depths of emotion and depression I went through in some of those diary entries was quite confronting. To relive them was almost heartbreaking."

During the writing process Gordon and Beachley formed a close relationship built on trust, understanding and respect, which is why she felt comfortable in revealing the truth of her birth.

"It was a little bit confronting, but I think I felt more worried about my mother than I did for myself," Beachley said. "I just remember being told and that was shocking enough, but I think it has been quite shocking for people to read about it.

"But I think it has given people a deeper understanding of who I am and where I have come from and what I have endured."