I’ve always known I was adopted. I was born in Busan, South Korea, but raised in France by parents who look nothing like me, with blond hair and blue eyes. My adoption records say I was born an only child to a very young, unmarried woman.

In December 2012 I was in London, studying fashion, when another student posted a YouTube video of me on my Facebook page. But I’ve never made a YouTube video in my life. When I watched it, I realised it wasn’t me at all, it was an American girl who looked exactly like me.

I watched the video over and over again, looking for differences, but we were identical, except for her clothes and her accent. Her name wasn’t on the video, so I had no idea how to contact her.

A month later, I was on a bus in Hackney when a friend told me there was a new video online of my doppelganger. I immediately watched it on my phone. It was a trailer for a film, so I looked up the cast and finally had her name: Samantha Futerman. I found out she was also born in Korea and her birthday was 19 November 1987, the same as mine. I was so shocked I had to get off the bus. I called my mum and she said the words I’d been afraid to even think: “Do you think she might be your twin?”

I spent a long time composing a message to Samantha, telling her to check out my Facebook photos. When she wrote back, she sent a picture of her adoption records. We had been born in the same clinic. Sam wrote, “Dude, we’re totally twins!” We started exchanging photos and then had a conversation on Skype. I was so nervous. We had the same mannerisms, the same laugh, even our hairstyle was similar. We talked about everything and nothing for three hours. After that, every morning I’d check her Instagram feed to remind myself she was real.

Dr Nancy Segal, a specialist in twin studies at California State University, contacted us when Sam started working on a documentary about us. She offered us DNA testing, so we swabbed our cheeks together on Skype, and we agreed to meet.

Sam, her parents and two brothers came to meet me in London last May. I took my mum and some friends for support. I was incredibly nervous. When I first saw Sam, I was trying not to stare, but she just started laughing. I went over and awkwardly poked her in the head – I just wanted to make physical contact. I didn’t know what to do. I wasn’t aware how small I was. Her feet looked tiny and I realised mine must be, too, and suddenly I knew how I looked from behind.

We wanted to be by ourselves, so we went to have lunch, and on the way we kept stopping to look at our reflections in shop windows. It was like a parallel universe. We’re so similar: she reacts to things the same way I do. We’re both awkward and have the same strange sense of humour. She doesn’t have to explain herself to me and she understands me perfectly, too. That night, we had a Skype call with Dr Segal, who gave us the DNA results. She said, “You should hug, you’re identical twins!” So we did. Around us, it was like somebody had won a football match. Everyone was cheering.

I would like to know why we were separated, but we still have no idea. Sam had tried to contact our birth mother before she knew about me, but the woman named on her adoption papers said Sam had the wrong person. I’m not worried about that, as I was never anxious to find my birth mother, and now I have Sam anyway. Sam lives in LA and I’m in France, so we meet when we can, spending special occasions together. We have discovered a love of surfing, so when I visit we often head to the beach. Our parents have become great friends and all say they have a second daughter.

I had a very happy childhood and never felt anything was missing, but there was one thing I wanted: to look like someone else in my family and to have that physical connection to someone. But what could be better than an identical twin? I’ll always have her in my life now.

• As told to Antonia Blyth.

Do you have an experience to share? Email experience@theguardian.com