Thirty-seven years ago, identical twins Begona and Delia were born at almost the same time as another infant named Beatriz in a hospital in the Canary Islands. Due to a hospital mistake, one of the twins was switched with Beatriz.

“This caused the single child [Beatriz] to grow up with the wrong set of parents and caused an unrelated pair of girls to grow up in a family thinking all their lives that they were fraternal twins,” says Nancy Segal, a psychologist at California State University, Fullerton.

 the twins didn’t meet until they were 28 years old — an observant retail clerk confused one of them for the other one, who was her good friend.

“A meeting was arranged for that evening, and it turns out that these two twins who had been separated for 28 years realized that they really belonged together,” Segal says. “DNA tests followed, the twin-ship was confirmed, and everyone’s life just fell apart.”

The twins themselves were also shocked and overwhelmed at the number of similarities they shared, despite being raised in separate environments with separate families.

read here:  http://www.npr.org/2011/08/15/138993130/learning-your-sister-is-someone-elses-twin