'She was so loving': Dead mum's partner speaks of her violent death

The Northern Beaches mother allegedly stabbed to death by her son had recently found her "soul mate" and was in love when the tragedy occurred, it has been revealed.

Lanell Latta's new partner was there when the alleged stabbing took place and says he has lost "a beautiful woman".

A day after the incident Ms Latta's devastated family have moved out of the Avalon home rented from Australian supermodel Gemma Ward.

After witnessing the ordeal on Monday, Geoff Robson-Scott has a black eye and a broken heart.

"I was there, I saw it," he told Seven News.

"She was such a beautiful woman, she was beautiful in spirit, the kindest person I've ever known.

"She was so loving."

Seven News has learned details about the conversation that sparked the alleged confrontation.

Lanell allegedly went into her son's bedroom to give him a pep talk and encouraged him to be "more positive in his life".

She then left his room and went to another part of the house with her partner.

Her son then allegedly walked up to his mother and with a single fatal blow, plunged the knife into her chest before walking off.

Geoff Robson-Scott followed his partner's son into the street, where police will allege an assault then occurred that left Geoff with a black eye.

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"I've just turned 60 and it's taken a long time to find that level of love," Mr Robson-Scott said.

"She was so happy, I was so happy, we were so close."

Latta's 25-year-old son was arrested nearby and last night charged with matricide - the taking of his own mother's life.

He did not apply for bail and is due back before a magistrate next week.