SINGAPORE - A 63-year-old man's sex abuse of his young grandson came to light after a seemingly ordinary conversation between the eight-year-old and his mother, who was reminding the boy to go to bed early.

The woman told the boy that if he could not wake up the next morning, he would have to stay at home with his maternal grandfather while the rest of the family went out.

This prompted the boy to confide in her that he did not want to be alone with his grandfather because the man had molested him.

On Thursday (Feb 22), the man pleaded guilty in the High Court to one charge of molestation and one charge of aggravated sexual assault by penetration.

Three other charges - one for molestation and two for showing a pornographic video to the boy - will be considered during sentencing.

He cannot be named to protect the identity of the boy.

The case has been adjourned to April 4 for mitigation and sentencing arguments.

The boy was between seven and eight years old when he was abused by his grandfather between 2015 and 2016 in the family's four-room flat.

One afternoon in early 2015, the man called the boy to his room and fondled him. When the family's domestic helper called for the boy, the man panicked.

He told the boy to get dressed and warned him not to tell anyone what happened as it would "create problems" with his parents.

In December that year, the man was sent to a drug rehabilitation centre. He was allowed to return to his family in September 2016.

More than a week after he returned, on Sept 28, the man sexually violated the boy in his room while they were alone at home. He again warned the boy not to tell anyone what had happened.

But the abuse was inadvertently revealed a month later, on Oct 22, when the boy's mother asked him to go to bed early.

After the boy told her he was touched inappropriately by his grandfather, the woman confronted her father, who admitted his wrongdoing and sought her forgiveness. A police report was made the next day.