Melanie Mertzel was 23 years old when a woman visited her parents' restaurant and asked: 'Are you adopted?'
The woman didn't understand why Mertzel didn't recognise her, leading her to make - and voice - that assumption.
Mertzel lied, telling the woman, 'No.'
"I don't go around saying that information," Mertzel told 60 Minutes on Sunday night. "Then, a week or two later, she came in with a picture of Ellen."
The photo of Ellen Carbone looked eerily similar to Melanie Mertzel. She remembers her boyfriend being astounded, saying "That's you," to which she responded, "That is not me."
"Don't tell me who I am. I know who I am," she remembers saying.
But she was intrigued by this near-identical girl in the photo. The woman passed on Carbone's details, for her to contact if she wished.
"When I went home from work that day, I called Ellen [Carbone] and when I heard her voice, I was like, "Oh my god. You sound just like me.' And then we started talking about everything," Mertzel told the Channel Nine news program on Sunday night.
Over the phone, they realised they had the same birthday, identical laughs, and they both had been subject to testing growing up.
The girls were adopted through an agency called Louise Wise Services, which told the respective adoptive parents that their daughter was part of a child development study. Until they were about 13 years old, a psychologist had visited their homes every few months to 'test' and 'study' them.