A PATERNITY suit filed by a man contesting child support payments for a set of twins took an unexpected turn after the results of a court-ordered DNA test came in.

They revealed that the man, identified only by his initials, AS, for legal reasons, was “almost certainly” the father of one of the twins — but not the other.

New Jersey Superior Court Judge Sohail Mohammad ruled that the babies had been fathered by two different men in a case he described as rare but not without precedence.

The mother, known as TM, gave birth to twin girls in January 2013 and named AS as the father when she applied for public assistance.

A legal battle began after AS disputed the claim on the grounds that their sexual relationship had not been exclusive. After TM admitted she slept with another man in the same week she had sex with AS, social services ordered a DNA test.

When the results arrived in November, they shocked both parties. In a ruling handed down earlier this week, Judge Mohammad said it was possible for a woman to have two of her eggs fertilised by two different men if she had sex with both during the same menstrual cycle.

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He cited two other cases, both in the US, that had gone through the courts.

DNA expert Dr Karl-Hanz Wurzinger testified that according to his own research, the incidence of twins with different fathers occurred in about one in every 13,000 paternity cases involving twins.

Judge Mohammad ordered A.S, who represented himself in court, to pay $28 (AUD34) a week in child support payments to his half of the twins.