Gary Watt in the Ngaio home he used to share with Anne Roberts, whose picture hangs on the wall, near her ashes.

The children of a Wellington woman who died without a will were forced to take their stepfather to court after he denied them their inheritance and blew some of the money on luxury items.

James Roberts-Gooch and his sister Alexandra Gooch were just 16 and 14 respectively when their mother, Anne Roberts - former private secretary to National MP Maurice Williamson - died of cancer in 2012.

Her de facto partner, Gary Bryson Watt, became the administrator of the estate, which included substantial life insurance and savings, but instead of divvying up the estate he splurged out, going on a cruise where he met his new girlfriend, and buying a motorbike, jetski and car.

SUPPLIED Anne Roberts died in 2012 without leaving a will.

The children were entitled to two thirds but Watt withheld the money and told them they weren't welcome back in the family home, which went to him as co-owner.

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Four years after their mum's death, the children still haven't seen a cent, despite the Family Court ordering last year that Watt pay them almost $300,000.

SUPPLIED James Roberts-Gooch and his sister Alexandra Gooch were entitled to two thirds of their mother's estate.

Watt still lives in the Ngaio home the family once shared, valued at $580,000, and is unapologetic.

"Yes I bought [the items], they're long gone," Watt said.

"Through loans, through investments and stuff I lost it, so it was pretty piss-poor management. I'm guilty, there you go."

DAVID WHITE / FAIRFAX NZ Watt admits failing to pay his stepchildren their rightful share of their mother's estate.

Under intestacy rules which apply when someone dies without a will, Watt was entitled to his partner's personal chattels, $155,000 and a third share of the rest of the estate.

James Roberts-Gooch, now 20, has applied to have Watt made bankrupt so the house can be sold and he and his sister paid the money owed, despite understanding that, once their legal fees are paid, there won't be much left. Watt accepts that a sale of the house will be the outcome.

Despite battling cancer several times, Anne Roberts never made a will and her son believes that was because she didn't expect to die so quickly.

SUPPLIED Gary Watt's new partner Heather Duffy on a jetski he bought.

"I used to say, 'you're sick, mum', but she always said 'Gary will always do the right thing by you kids'."

Nicola Peart, a professor of law at Otago University, said the case highlighted the importance of having a will and making sure children were catered for.

"Especially when you have a partner who's not the father of the children. She quite clearly had no idea that he would do this to her children."

SUPPLIED A picture from a cruise Gary Watt took. Watt says the cruises were him "being ridiculous, trying to forget".

When Anne Roberts died, James was in Australia with his father, while Alexandra was living at the family home.

Watt made his intentions clear soon after the funeral, James said.

"He said 'don't think you're getting anything of your mother's' and 'this is the last time you'll ever come back here, it's now a bachelor's pad'."

Watt said he only remembered saying "please go home" as he didn't want a wake, and by "bachelor's pad" he meant it was now him and the dog.

Alexandra dropped out of Wellington Girls College and the siblings moved to Queensland to live with their father.

Watt wrote offering them $30,000 each, but James felt they were being ripped off. His mother had worked at Te Puni Kokiri, Land Information New Zealand and as Williamson's private secretary.

"There was something inside me that said this was not right. Mum worked hard for so many years and earned really good money, how the hell could this be the case?"

He started doing research on family law.

"I found it really hard to understand a lot of the jargon. It's like you're just being told 'this is the law' by an adult and that's it."

He could see on Watt's Facebook page that he had been on cruise ships with his new girlfriend and there were photos of a Triumph motorbike, a jetski and car.

James dropped out of school and started working at a cafe to save money for legal fees, moved back to New Zealand and enlisted Wellington firm Ord Legal.

In August 2015 the Family Court ordered Watt to pay $149,000 each to James and Alexandra, and in February a charging order was put on the house, so they could be paid from Watt's share of the sale of the Ngaio property. An application was also made to bankrupt Watt.

Watt wouldn't say how much money he took from the estate, but admitted he had lost most of it.

He said he didn't consult a lawyer when he became administrator but did research on the internet and thought they were owed $30,000 each.

"I'm quite happy to take on the chin that I had it wrong."

He had sold the motor vehicles. "Just to put James' mind at ease, he's not getting his hands on it."

Watt said Anne hadn't asked him to look after the children after she died.

"The kids have a gripe, thats fair enough. I'm not withholding it purposefully for the fact I don't like the little bastards," he said.

"The kids treated me like rubbish, a couple of times I spoke up but I couldn't do anything about it."

He said he and Roberts had made draft wills but never got around to signing them.