A wealthy Christchurch businessman's mistress of 27 years has been barred from claiming a share of his multi-million dollar divorce payment.

The woman had sought to appeal a court ruling which said she wasn't the businessman's de-facto partner and therefore not entitled to a share of relationship property.

After the wealthy businessman and his wife split in 2007 after 47 years of marriage, he faced two relationship property claims in the Family Court - one from his ex-wife and the other from his mistress and long-serving employee.

The value of the relationship property at issue was somewhere between $22 million (on the wife's calculations) and $16 million (on the husband's).

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The businessman's affair with his mistress began around 1980 and she began working for his company the following year.

She has worked there ever since, according to the High Court.

Evidence before the Family Court indicated that throughout his marriage, the businessman had other sexual relationships with other women. His wife was unaware of all these affairs and when confronted he always denied them.

According to his ex-wife, the businessman's affair with his mistress was clandestine. It took place in early mornings or when he left family holidays to return to "work".

The man, according to the High Court, in 1998 told his wife he was participating in a yacht race in Australia and even purchased wet weather boating gear to support this ruse.

He was, in fact, spending a holiday with his mistress in Perth.

The wife alleged in the High Court that the mistress and her ex-husband's claim they were in a de facto relationship only surfaced in 2011 or 2012, specifically to assist him opposing her in the Family Court.

The mistress argued she was pursuing her entitlement and that her relationship with the man was a devoted one, in which she had a strong focus and passion for his business.

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The mistress rejected the assertion she manufactured the de facto relationship argument late in the piece, that she colluded with her lover on this and that she had done so to keep his business interests in his hands.

The Family Court's Judge Anthony Walsh last year found there was no qualifying de facto relationship between the man and his mistress.

This, and other parts of that decision, was then appealed to the High Court, but Justice David Gendall agreed in June that the relationship between the man and his mistress was not a de facto one.

The man and his mistress sought leave to take the case to the Court of Appeal, but Justice Gendall denied this bid earlier this month.

"I have not been moved to the point where I consider there to be any interest, public or private, sufficient to outweigh the expense and delay of a further appeal here," Justice Gendall said.

"Two Judges have presided over this proceeding which has been the subject of extensive examination before both the Family Court and this Court, and they have both then reached the same substantive conclusion. Further, this proceeding has its origins in events occurring over eight years ago. There is a need for finality in litigation. In my view, the time has come for that finality to crystallise," he said.