The grandmother of a murdered five-year-old boy says she felt trapped in a violent relationship that she could not escape from.

Maria Pienaar is now left grieving the brutal loss of her grandson at the hands of the very man who allegedly controlled and abused her for months.

Pienaar (45) met her partner six months ago in the city. She described their relationship as violent and controlling, characterised by assaults even during intimate moments.

Pienaar said at some point she would feel like a hostage, unable to break away from the relationship, and has lived in fear since then.

The bruises on her body are a result of another episode on Saturday evening. That episode is the evening Pinaar's five-year-old grandson was murdered, allegedly by her partner.

Pienaar narrated that before the incident, her partner asked her to accompany him to the truck port in the Prosperita Area to sell personal belongings.

But along the way, she alleged that his calm behaviour had transitioned to hurling insults and threats to kill her.

The 35-year-old suspect also turned his anger on the five-year-old boy in their company, and what followed was tragic.

"He picked him up like a bag of cement and smashed him against the concrete. There was no one around; no one could hear me scream," said Pienaar.

Through tears, she narrates that the five-year-old Romeo, who stayed with her temporarily, was a joyful and loving child.

That evening, Pienaar returned home alone, mourning the absence of the joyful child.

"He had a knife that was bigger than my arm. I really do not know what triggered him, though. The death of my grandson is extremely painful. I feel a certain sense of relief that he has been arrested; at least now my body and soul can rest."

Pienaar claims that the man has a history of substance abuse, which appears to have led to brutal assaults; any attempts she made to intervene or protect herself only worsened the situation.

She said that on the night of the incident, the suspect had been drinking too.

The 45-year-old woman recounted that, at one point, the suspect threatened her with a knife and told her he would remove her heart.

The 35-year-old suspect is reported to have lost his mother to criminal acts, and he was the one who had to identify her body. He was a teenager then.

His young brother, too, reportedly died in a fire.

The family of Pienaar is largely unaware of any other relatives he may have. 

The once casual domestic worker is now charged with the murder of the five-year-old Romeo and is expected to appear in court this week.