A Brisbane woman had her “worst fears” realised after finding out she was the product of incest – a daughter born from her mother and her maternal grandfather.

Lois Buch, who was adopted to a Brisbane family when she was young, made the discovery after making contact with her birth mother, who refused to give her details about her father.

After her birth mother died from cancer and she was still left without answers, Ms Buch, 47, contacted one of her mother’s siblings for the truth.

“My birth mother has a lot of siblings, and her youngest sister is my age,” Ms Buch told SBS’s Insight program.

She told the program she contacted the youngest sister over a private message on Facebook, and received a response in the same day.

“She replied within 24 hours and said ‘I will tell you, I agree you deserve to know but you have to come to Sydney and see me face-to-face’,” Ms Buch said.

Ms Buch was told to “prepare for the worst” and said the revelation that her biological grandfather was also her father was her “worst fears” confirmed.

The repeated rape of her mother saw Ms Buch given up to her adoptive Brisbane family.

She also told the program her biological mother had a second child in the same horrific circumstances.

The secret remained within the family for a number of years, and no charges were ever laid against her biological father.

Around one-in-five Australian women have experienced family violence.