In December 2012, Anais Bordier thought she was staring at an image of herself when she saw a YouTube video featuring a young woman who looked just like her.
"I wondered, 'Who posted a video of me on YouTube?' Bordier, who was raised in Paris but living in London at the time, tells PEOPLE.
When Bordier, 27, a budding fashion designer, looked at the image again, she realized that it wasn't her at all. It was a young woman from the United States.
When she found her lookalike's name in the credits of a movie trailer, she was stunned at what she learned: that she and the other young woman, Samantha Futerman, 27, were both born in the South Korean city of Busan on Nov. 19, 1987 – and that they were both adopted.
"It was shocking," she says.
Bordier grew up as an only child and said, "Sometimes, as a kid, I felt lonely and I didn't know why."
In February 2013, when she reached out on Facebook to Futerman, an actress who lives in Los Angeles, she learned not only that she had a sister, but an identical twin.
"I immediately thought she was cool because she made a Lindsay Lohan reference from The Parent Trap," says Futerman about the 1998 remake of the 1961 film about identical twin girls who live on two different continents and find each other after being separated at birth. "I thought it was cool that we could be twins."
Bordier learned that her twin grew up in New Jersey with three older brothers – and that she is a tomboy.
Related: Youtube Stars 'The Rhodes Bros' React to Ingrid Nilsen's Coming out Video
"Deep down inside I think I was more of a tomboy, too," says Bordier. "I always had more guy friends than girlfriends."
Last year, the sisters wrote a book about their incredible journey, Separated @ Birth: A True Love Story of Twin Sisters Reunited.
Now have also shot an award-winning documentary called Twinsters chronicling the moment they met, how they have forged a relationship over two continents (they talk all the time) – and the close bond they share as twins.
Well before a DNA test confirmed that they were identical twins, says Futerman, who co-directed it. "We were documenting everything. We were taking screen shots and stuff like that. Then a friend of mine said, 'You have to make a movie about this. You have to share this.
"I said, 'Anais. Do you want to share our story?' She said yes and then we made the commitment to doing it."
The sisters, who love to laugh at the same time, have worn their hair the same way since they were kids and both hate carrots, are excited for the documentary's premiere Saturday in New York.
"It's going to be fun!" says Futerman, erupting again into giggles, along with her sister. "These past two and a half years have been fun!"