Non-identical twins Emilie Falk and Lin Backman - strangers until last year - were separated nearly 29 years ago when they were separately put up for adoption in Indonesia.
According to a DNA test the pair had done two months after reuniting in January last year, there is a 99.98 per cent chance of them being sisters.
A complex string of events led up to that revelation.
Both women were adopted from an orphanage in Semarang in northern Indonesia by Swedish couples, but there was no mention in either of their documents of the fact that they had a twin.
When Ms Backman's parents left the orphanage with her all those years ago, the taxi driver had turned around and asked them: "What about the other one, the sister?" and they jotted the girls' Indonesian names down on a piece of paper.
The name helped Ms Backman's parents track down the Falks back in Sweden, and the two families got together a few times when the girls were babies to compare notes.
"They went through the adoption papers, but they didn't think we were very similar and there was a lot in the papers that didn't add up ... And there were no DNA tests back then," said Ms Falk.
Among the discrepancies were different names for the girls' fathers. And although the records showed they had the same mother, the families eventually decided that this too was an error.
The two couples in the end wrote off the idea and eventually lost touch.
Although their parents had told them the story as children, both Ms Falk and Ms Backman later forgot about it. Growing up, neither was interested in information about their biological background, so they never asked.
"But when I got married two years ago I started thinking about family and my adoption, and when I asked my mother she told me this story again, and I decided to look for Lin," said Ms Falk.
She had a name and began searching through a network for Indonesian children adopted by Swedish families, and found Ms Backman on Facebook.
"I am born on March 18, 1983 in Semarang and my biological mother's name is Maryati Rajiman," Falk said she wrote, and quickly received the reply: "Wow, that's my mother's name as well! And that's my birthday!"
1 day ago