When a set of Vietnamese male twins came out looking almost nothing alike, the family suspected there had been a mix-up in the hospital nursery. As they grew, their striking differences in appearance became harder and harder to ignore: One had thick curly hair, while the other's was straight and thin.
Finally, relatives convinced the parents to have the boys tested to see what was behind the differences in their looks. Lab results confirmed that the truth behind the boys’ contrasting features was even stranger than what the family had originally suspected. Although the brothers were born at the same time to the same mother, they had different biological fathers due to a rare occurrence known as superfecundation.
Biologically speaking, two twins, or siblings born at the same time, can have different fathers as a result of superfecundation. This occurs when a woman has sexual intercourse with two different men and sperm from each fertilize two separate eggs during the same menstrual cycle. Though rare, this is not the first time the phenomena has been documented. Back in 2015 a New Jersey judge ruled that a father would only have to pay child support for one of his twin girls because the other was not biologically his own.
Le Dinh Luong, president of the Genetic Association of Vietnam, the site where the boy’s genetic testing took place.The family was indeed surprised by the test results, but declined to give more details on the case due to its personal nature.