A man is facing deportation after he allegedly married his sister in an attempt to get a visa.

The 28-year-old from Cambodia always denied he and his "wife", from whom he had since separated, were related. But the pair had repeatedly refused to take a DNA test.

The man took his case to the Immigration and Protection Tribunal after Immigration New Zealand (INZ) declined his application for a student visa because he allegedly previously lied to authorities.

According to a tribunal decision, the man came to New Zealand in December 2013 on a one-year partnership visa, after marrying a Cambodian-born New Zealand citizen in Cambodia.

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In July 2014, the man applied for residency on the basis of the partnership.

INZ declined the application because it believed the "couple" may in fact be siblings, but granted him a partnership visa.

A person who asked INZ to keep their identity secret claimed to have known the wife for many years.

The informant said the woman and man were siblings and the "wife" had been in a long-term relationship with another man.

123RF The Immigration and Protection Tribunal said the man had made "a well-planned and sustained attempt to deceive Immigration New Zealand" by allegedly claiming his sister was his wife.

The person also alleged colleagues in a cafe where the "couple" worked knew them as brother and sister but the wife had told them to tell anyone who asked that the man was her husband.

INZ also interviewed a real estate agent who said he had known the "wife's" stepfather for many years and that the stepfather had asked him to find a rental property for "his son and daughter".

The real estate agent told INZ the "husband" had confirmed to him that he and the first woman were siblings.

INZ had also become aware of comments on the man's Facebook page referring to his "wife" as his sister.

The man applied for residency again, before withdrawing the application.

He then applied for a student visa, which INZ declined. His interim visa expired and he remained in the country unlawfully.

The man tried several times to have the decision reversed. He asked the Immigration Minister to intervene, complained to the Ombudsman and appealed to the Immigration and Protection Tribunal.

He claimed he was "the victim of false allegations" and had a new partner and a child, who would face hardship if he was deported.

All his bids to have INZ's decision reversed failed.

The tribunal concluded on the balance of probabilities, the man's marriage to his former wife was not genuine and their true relationship "was that of siblings".

It said the man made repeated false and misleading statements to INZ over almost five years and dismissed the appeal.

It described the man's actions as "a well-planned and sustained attempt to deceive Immigration New Zealand" in order to get a residency visa, to which he was not entitled.

The man is now liable for deportation.