A man trying to get his hands on the seven-figure inheritance of his late mother's partner has lost his appeal.

John Mathieson and Paul Blumenthal weren't father and son, but they acted like it.

Mathieson and Blumenthal's mother were de-facto partners for 22 years, and Mathieson - who never had children of his own - treated Blumenthal like a son.

Even before Blumenthal's mum and Mathieson became a couple, the pair had bonded over their shared interest in cars.

Advertisement

After her death Blumenthal and Mathieson remained close. Mathieson was best man at Blumenthal's wedding, and Blumenthal helped out around the property like any good son would do for his father.

And in the final weeks of his life, Blumenthal tried to make Mathieson as comfortable as possible.

According to Blumenthal, his de-facto dad had often expressed a desire to leave part of his estate to Blumenthal and his children, who considered Mathieson their grandfather.

But when Mathieson died in February 2014, aged 72, Blumenthal was stunned to find he wasn't given a cent in the old man's will - it was all going to charity.

His surrogate father had put his money in a trust, which owned the property he lived on, and the beneficiaries were himself and the Neurological Foundation of New Zealand.

When Mathieson died, the trust's assets of $453,000 went to the foundation, as did another $470,000 under his will.

In 2015 Blumenthal went to court to claim money from the estate, claiming Mathieson had expressed a desire to leave him an inheritance.

Mathieson had planned to update his will but had never got the chance, his lawyer said at the time.

However, Mathieson's lawyer gave evidence that during regular annual meetings with his client there was nothing to suggest he wanted to make any changes.

The Court of Appeal said at the heart of the case was the claim Blumenthal's contributions had been undervalued and the benefits received overvalued.

"We have not been persuaded this is correct, and along with the Judge see the imbalance, if any, as having favoured Mr Blumental," read the judgment.

The court said the greater need flowed to Blumenthal whom Mathieson supported through two difficult divorces. He also used the property for storage and even ran a business from it.

The chores Blumenthal did around the property also did not warrant any special recognition other than what would normally occur in a family.

Also, the special care given in the final weeks of Mathieson's life was not recognised as exceptional.

Blumenthal had to go out of his way to visit his ailing de facto father but there was nothing to merit anything other than minimal recognition.

In dismissing the appeal the court found there was not the necessary level of uncompensated effort to support the claims made.