A pair of Vietnamese twins have been found to have different fathers. As remarkable as this is, the strangest thing about this story is that it isn’t the first time in the world that this has happened, according to BBC News.
When the two non-identical brothers were born, their family noticed that one of them looked nothing like his relatives. After a routine DNA test, it was confirmed that the two babies were indeed half-brothers.
Non-identical twins occur when two egg cells are fertilized by two different sperm, but both sperm cells almost always belong to the same man. This far rarer type of pregnancy, known as heteropaternal superfecundation, occurs when a woman’s eggs are fertilized by two men within a very short period of time – generally within 48 hours.
Professor Le Dinh Luong, president of the Hanoi-based Vietnam Genetic Association that conducted the DNA testing, told BBC News that “there are only less than 10 known cases” of this type of truly bizarre birth. “There might be other cases but the parents and/or the twins were not aware of it or didn't want to announce it,” he added.
As odd as this is, stranger things have happened. Last year, a man failed a paternity test because his unborn twin turned out to be the biological father of his son.