ABC News' Rich McHugh reports:
Imagine growing up as an adopted child, and at age 25 getting at Facebook message from a stranger who looks exactly like you.
That's what happened to Samantha Futerman, an actress living in Los Angeles.
"On February 1st, 2013, I got message on Facebook from a girl in London," Futerman said. "It said she had seen me in YouTube video, then after looking my name up online, saw that we were both adopted, and born on the same day, in the same city. When I saw her profile, it was crazy. She looked just like me."
The girl who had sent the message was Anais Bordier, a French fashion designer in London.
"When I looked at the video, I - it was, like, shocking …," Bordier said, explaining her reaction to seeing Futerman's YouTube video. "You can't imagine that you might have a twin sister somewhere that you don't know about."
So she sent the Facebook message. Bordier and Futerman would discover that they were both born in Busan, South Korea.
It begged the question: were they twins who were separated at birth?
They decided to chat via Skype. Both women speak English, although French is Anais' first language.
In an interview with "Good Morning America" co-anchor Josh Elliott, Futerman described looking into Bordier's face and seeing a mirror of her own features.
"It was weird, but I feel like there was a strange calm and comfort as well, and something that I can't really explain," she said. "We talked for three hours."
They shared their life's stories, talking about baby pictures, allergies, boys and food.
"And then, she's, like, 'I have to pee. I've got to go.' I was, like, 'Me, too. I've got to go, too,'" Futerman recalled while laughing.
When they met for the first time in London, Bordier poked Futerman's head to make sure she was real.
The met again in Los Angeles, where they enjoyed the beach, baseball and some In 'N Out Burger. And they united again in Manhattan.
They had their DNA tested to erase any doubt.
The result proved what their faces told them all along: they were sisters.
Bordier said she had always felt as though something was missing in her life. She never knew that, after she and her sister were born, they were each placed in separate foster care agencies and adopted separately.
"I did feel like I missed something," she said. "I had an imaginary friend when I was a kid. It happens to a lot of kids, but I had an imaginary friend and she was called Anne … I needed that comfort, I guess,"she added.
Asked how knowing the truth had changed her, Bordier replied: "I think I feel a lot more confident knowing. It's like, yeah, I've found my second half back."
Futerman has two adoptive brothers, while Bordier is the only child in her family.
The sisters have decided to make a documentary about their experience, and they say they've already heard from many other adoptees who are thankful to them.
"It makes me really emotional, because as a kid you have dreams of wanting to change the world. It's something- it's something that feels too far away … it's an overwhelming thing to know that two little, tiny, Asian hobbits can, you know, make a difference," she said, laughing.
For Christmas, Futerman got necklaces that say "Best Friends Forever" for her and her sister. Bordier appreciates it.
"It sounds really cheesy, but I think we need those little kid's moments and those cheesy moments together," Bordier said.
Futerman described finding her sister like "that feeling on Christmas when you open up the presents, the one you were asking for, it's that - that pure feeling of joy … that's how I always feel."