An unidentified woman in Hanoi, Vietnam, gave birth to bi-paternal twins, which are twins with different fathers.
“Our Center for Genetic Analysis and Technology lab has tested and found a pair of bi-paternal twins,” Le Dinh Luong, president of the Genetic Association of Vietnam, told Agence France-Presse.
“This is rare not only for Vietnam, but for the world,” Luong added.
The woman's husband asked for the children, now both 2 years old, to undergo genetic testing because he wanted to know if he was the biological father of both, Vietnam's government-run Tuoi Tre newspaper noted.
The husband's family pressured him to request the DNA testing because one of the children looked different than him and the other child.
The DNA test confirmed what the relatives suspected. Additionally, the wife was found to be the mother of both babies, which proved there was no mix-up at the hospital.
Bi-paternal twins can happen if the mother ovulates two eggs at the same time, and the eggs are fertilized by two different men.
One of the twins reportedly has fine and straight hair, while the other child has thicker, wavier hair.
In 2009, Mia Washington gave birth to bi-paternal twins, Justin and Jordan Washington, in Dallas, reports The Telegraph.
Justin and Jordan had different fathers because Mia conceived them with two different men during the same ovulation period.
Mia and her partner James Harrison had the DNA tests done because Justin and Jordan looked different at 11 months old.
"I have twins, but they're by different fathers," Mia told Fox News at the time.
"Out of all the people in America and all the people in the world, this had to happen to me," she added.
"This is likely to be the only time that we will ever see this occur in the city of Dallas; it's that rare," Dr. Chris Dreiling said.
The story had a happy ending. Harrison forgave Mia's infidelity and said he would raise both boys as his own.
Mia planned to tell the boys they had different fathers when they are old enough to understand, but was not going to tell the other father, although he may have found out via the news.