You may think you aren't in a de facto relationship, but the courts may have a different view.
The warning from the Public Trust comes after a landmark case in which an Auckland man was awarded $300,000 from the estate of a woman who described him as her "friend" but whom he claimed he was in a relationship with for 27 years.
The Public Trust says the case demonstrates why people should update their will regularly.
Justice Grant Powell ruled Steven Moon and the late Mary Doyle were in a de facto relationship, despite Doyle repeatedly listing herself as single on formal documents, and therefore Moon was entitled to a portion of Doyle's estate.
When she died in January 2017 from cancer, Doyle left her Fairview Rd house to her brother Patrick.
Moon got only Doyle's ashes and a note that said: "I'm leaving you the most precious thing: me (even though it's in a box)".
Moon, 62, told the High Court at Auckland he had been expecting to receive Doyle's entire estate and was "upset and felt used".
"I do feel that in death Mary should have put me first as I put her first in life. I
feel betrayed by her," he said.
"It was as if I was nobody in her life. I had spent nearly every day with her for 27 years, except for two and a half weeks when I was in hospital and some short trips to the South Island."
Although the pair did not live together for most of their relationship they had looked after a property together in the 1990s.
Moon said he would often pick up groceries for Doyle as well as cook dinner for her, give her her medication, get her changed for bed and do chores around her home.
He said he would kiss her goodnight before going to his house to sleep.
Moon claimed for Doyle's whole estate which Patrick challenged, claiming Doyle and Moon were not in a de facto relationship.
When asked by the Public Trust if Moon was her partner when Doyle was composing her will she said he was a companion only, Patrick said, according to the High Court decision released this week.
Maxine Blake, a childhood friend of Doyle, said she never thought Moon was just a platonic friend.
"I was not living with Mary, but I always understood that they had a romantic
and sexual relationship."
Powell said he believed Doyle and Moon were two private people who formed a relationship that worked for them despite very considerable difficulties arising from Mary's medical conditions".
The $300,000 payment from the estate he awarded to Moon would almost certainly require the sale of Doyle's house.
Public Trust spokeman Josh Byers said the organisation, New Zealand's largest trustee service, advised its customers a court could decide they were in a relationship even if they did not believe they were.
"In advising on matters such as a will we ask specific questions relating to relationships and the nature of these.
"It's important that firstly people have a will, the advice they receive is from an expert, and the information provided is up to date given their current circumstances.
"Also they should always check their will as their circumstances change to ensure it is still suitable for their new situation."
A change in circumstance could include the birth of a child, marriage or divorce.
Wills were occasionally challenged but disputes did not always make it to court, Byers said.
"Public Trust would not pursue an appeal unless the beneficiaries considered that appropriate and that would also be subject to obtaining legal advice on the likelihood of success of any appeal."