When Fiona Darroch started looking for books her godfather had written, she never expected what she would find - that the man was actually her biological dad.
Dr Norman "Tony" Walker - an obstetrician who had also delivered her - had actually used his own sperm when Darroch's mother was artificially inseminated.
The discovery came about when Darroch found a strange review on Amazon six years ago, news.com.au reported.
In the review section about a book Dr Walker had written, Anne Crossey in Ireland wrote that he had been her mother's sperm donor and she was after more information about him.
Crossey had unknowingly helped uncover a secret. Dr Walker had been using his own sperm at a time when fertility treatment was taboo and sperm donations were rare.
Woman who were artificially inseminated were not given details and were apparently unaware Dr Walker was the donor.
Darroch, 57, decided to get in touch with the woman because she had lots of letters her "godfather" had written to her as a child and had been given all his war medals and lots of photos.
"At that stage I had absolutely no idea of my true story," she tells SBS Insight tonight.
"When I fished out his letters, I found a driver's license of his that he had given me from when he was 16. And I showed it to my husband and said, 'Who does this look like?' and he just laughed, because it looks exactly like our youngest daughter.
"I went and had a chat to my mum and I said, 'Look, something's going on here and I'd like you to tell me the truth'. My mum came clean and told me that they had used a sperm donor, and that Dr Walker was her gynaecologist."
Darroch is originally from South Africa and because Dr Walker had killed himself in 1977 it was hard to find out more information. Her mother didn't know much about the donor process.
It wasn't until Darroch's daughter took a DNA test three years ago that she finally had confirmation.
It turned out Dr Walker had used his own sperm in countless cases.
"When the results came out, (my daughter) had matched with lots and lots of people and she didn't have a clue who they were," she said.
"It just so happened that one of my donor (half) siblings had given his entire family ancestry tests for Christmas that year, and we all matched at the same time."
Darroch and her half-brother then started putting the pieces together.
They were able to speak to one of the clinic staff who worked with Dr Walker, who confirmed that Darroch was not the first.
"My youngest most recently discovered (half) brother is 14 years younger than me, so he must have done it for at least 15 years perhaps longer," she said.
"So we're thinking maybe 200 to 300 (half siblings)."
The siblings she has identified are in the United States, Ireland, New Zealand, the UK, South Africa and Australia.
It was like losing my own father who raised me all over again," she said.
"You experience the same grief and loss, because you're no longer connected to the person who you thought you were connected and then find out you're connected to all these new people. It's quite tumultuous. It's a very difficult path."
In 2018 Darroch and her donor siblings who share the same mother, as well as a half-brother and sister pair from the US met in Australia for the first time.
The half-brother, named Greg, was raised believing he was of German descent, and had done a DNA test with the same company.
"My test came back showing that I hadn't had a German ancestor in five generations. This was clearly a surprise," he told the Sunday Times.
"My dad died in 2000 so I couldn't ask him. And then Fiona's daughter suddenly showed up on the site as being my niece.
"I got in touch with Fiona and she explained it all. I knew she was right because Dr Walker was a family friend. I remember how upset my mum was when she found he had died."
Dr Walker's biological children and grandchildren have not had genetic testing to definitively confirm the link with any donor children.