In an extremely rare occurrence, a mother in Vietnam has learned her fraternal twins have different fathers.
DNA testing for the two siblings at a clinic in Hanoi revealed that they are bi-paternal twins.
There are few details available about the children and their parents because of a confidentiality agreement between the family and the clinic, CNN reported Monday.
Professor Le Dinh Luong, head of the agency that conducted the testing, told the BBC the results were "100 percent correct," albeit very unusual.
"This is rare not only for Vietnam, but for the world," he told Agence France Presse on Tuesday.
The scientific term for this highly uncommon occurrence is heteropaternal superfecundation. It occurs when a woman releases multiple eggs that are then fertilized by multiple men during a single ovulation period, meaning the children are conceived within a short time frame -- likely hours or days apart.
The case in Vietnam is believed to be the first of its kind recorded in the country, with less than 10 others documented worldwide.