What does it feel like to discover, in adulthood, that you are a twin? Here, five sets of brothers and sisters tell their stories of meeting for the first time – and what happened to them next

Imagine finding out late in life that there’s someone out there who looks just like you: same eyes, same nose, same mouth. Not a doppelganger, but a twin you never knew existed. Discovering that you’re a twin is “a life-changing experience,” says Nancy L Segal, a professor of psychology and the director of the Twin Studies Centre at California State University, Fullerton.

Segal has written nine books on twins and is now working on her 10th. Over the years, she has come across at least 100 pairs of reared-apart twins. In most cases the twins were separated at birth and adopted by different families. “Adoptees often feel that something’s missing in their lives,” Segal says. “I think it relates to the fact they don’t look like their family members. They don’t feel a certain kind of belonging, even though they’re loved. When they find a twin, they can see themselves in somebody else. And that’s important.”