Although the twins developed side-by-side in their mother's womb, DNA tests recently showed they came from two eggs fertilized by two different men.
Le Dinh Luong, president of the Genetic Association of Vietnam, told AFP that this is an extremely rare example of when eggs are fertilized during separate acts of sexual intercourse within the same ovulation period.
"Our Centre for Genetic Analysis and Technology lab has tested and found a pair of bi-paternal twins,” he said. “This is rare not only for Vietnam, but for the world."
The report originated from the state-run Tuoi Tre newspaper, which reported that one of the fathers first requested a DNA test after his family pointed out that the twins, who are now two years old, looked very different from each other.
This isn't the first time this phenomenon has occurred. In recent years, it has been reported at least twice in the U.S.
Back in May, a New Jersey dad was ordered to pay child support for one girl in a set of twins after DNA tests proved he is not the father of both, CNN reported.
"This is a case of first impression in New Jersey and only a handful of reported cases exist nationwide," Judge Sohail Mohammed said in his ruling.
None of the parties were named in court documents.
In 2009, Texas mom Mia Washington got the news her twins had different dads after a paternity test was administered for the starkly different looking boys.
"Out of all people in America and of all people in the world, it had to happen to me. I'm very shocked," Washington told Fox News at the time.
