A New Jersey woman found out that her twins had been fathered by two different men in a Passaic County paternity case.

The woman, identified only as T.M., was applying for public assistance and named her romantic partner as the father of both children, the New York Times reports. In the course of testimony, she admitted to sleeping with a different man about a week after she believed she had conceived the twins with her partner.

This prompted a paternity test, which revealed that each man had fathered one of the twins, who are now toddlers. The original partner, identified as A.S., will now only pay child support for one of the children.

This kind of occurrence is rare, but not unheard of—a doctor testified that 1 in 13,000 paternity cases for twins involve two different fathers.

[NYT]

Read next: The Science of How Women Can Have Twins With 2 Different Fathers

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