The Belfast Crown Court jury of five men and seven women heard on Tuesday that the years of alleged rape and abuse culminated in the woman having three children to her step-father.
The 47-year-old, who cannot be identified to protect his alleged victim, is on trial accused of 12 sex offences including rape and indecent assault allegedly committed over an eight-year span between January 1997 and January 2005.
Opening the case against him prosecution lawyer Kate McKay described how the alleged abuse first began when the girl was around 11 or 12 years old.
However Ms McKay told the jury that the alleged abuse escalated and that the girl was raped by the defendant when she was around 15 years old.
"She would say that this sexual intercourse happened on a regular basis," claimed the lawyer adding that "she felt she could not break away".
The jury heard how the alleged victim gave birth to her first child when she was 17 years old and that DNA testing proved the child was fathered by the defendant.
The Crown case, Ms McKay told them was that obviously as a child the alleged victim could not have consented to any sexual contact between her and her step-father and also that from when she was 17 until she was 20, she did not consent to any sex or sexual contact between them.
"When she came to about 20, she just let it happen because she was so used to it," said the lawyer.
Arrested and interviewed, the 47-year-old denied doing anything wrong when his step-daughter was a child but that as she got older "they grew close" and had started a "consensual" relationship.
The trial continues.