The crimes occurred after the 53-year-old grandfather, who cannot be named, agreed to babysit the girl while her parents went to a birthday party.

The man had been drinking but assured his son that he was still OK to look after the girl.

The defendant still claims he cannot clearly remember what happened next.

But at some point, the court heard, he raped the young girl, before telling her to keep his actions a secret.

Supreme Court Justice John Burns said it was hard to imagine a "more serious breach of trust", and rejected the grandfather's claims that he had no memory of what he had done.

The three-year-old told her mother about the "secret" the next day.

The victim's dad called up his father, but the man denied the allegations, and said he was drunk and could not remember what had happened.

Police were called, and forensic testing of the girl's underwear found a close match to the DNA profile of herself and her grandfather.

He was later arrested and charged with sexual intercourse without consent with a person under the age of 10.

The girl's dad has since confronted his father, allegedly assaulting him while he was out on bail earlier this year.

The victim's father has since been charged over the assault.

The three-year-old has experienced lasting psychological harm due to the molestation, but thankfully suffered no permanent physical injuries, the court heard.

A pre-sentence report found the grandfather had a troubled childhood. He had an abusive father, and has experienced alcohol and cannabis abuse, and physical and mental illness.

He lived a solitary life, with only one real friendship, which has since ended due to the court case.

He did not have any criminal history, and has never been in prison before.

Justice Burns sentenced him to four years and two months jail.

He will be eligible for parole in March 2015.