Genetic Sexual Attraction (also referred to as GSA) is an awful, widely unknown concept. Often affecting members of a family who have been separated for most of their lives - usually due to adoption - it is something that a person can feel great shame about, while being unable to control their feelings.

The term was coined by a woman called Barbara Gonyo years ago, when she felt an overwhelming sense of sexual desire after being reunited with her birth son, Mitch, who was adopted as a baby.

Although there are a lot of unknowns about GSA - why it affects some people and not others, primarily - it is accepted that it does happen. Even though it feels pretty gross to hear about. Which is why this interview - with an 18-year-old girl who is now engaged to her own biological father, after not having seen him for 12 years - makes for some pretty uncomfortable reading.

What was your family like when you were growing up?

My parents had me when they were 18 — they met in high school and I was conceived on prom night. They were serious for about six months but broke up while my mom was still pregnant with me. My dad wasn't there when I was born. I think my mom's psychological problems meant the relationship never really worked out. She has bipolar disorder and some other mental health issues. They just weren't happy and didn't really keep in contact after I was born. She wanted to do it alone.

Did you have any contact with your father when you were a child?

He briefly came back into my life when I was about 3 or 4 and I saw him on weekends until I was about 5. He lived about an hour away from us and my parents constantly argued about visitation. He was always doing the drive to see me because my mom wasn't very fond of it — she wouldn't even meet him halfway.

Can you remember much from your time with your dad when you were little?

I have some memories. He spoiled me rotten. I had this giant storage tote of Barbie dolls and I had my own Mary-Kate and Ashley bedroom. It was a little girl's dream. We'd sit in the yard blowing bubbles together, and he took me to the zoo where he bought me a stuffed animal that I kept until I was 16. I ended up washing it and stupidly put it in the dryer, which melted all its fur. I remember he gave me a miniature tea set. I still have it.

Why didn't your father try to get in touch with you?

My mom said that he didn't want to have anything to do with me. But she was very controlling and kept me under Fort Knox–like conditions. She's had my Facebook password since I've had an account. One day, after I got my Facebook privileges back, he added me as a friend. At first, I figured it was my grandpa because they have very similar names. I thought, Maybe Grandpa got techy?

Then I realized it was my dad. I was like, Oh my God, where have you been? I don't know if I can get close to you. I told him I thought he was dead and asked why it took him so long to contact me. He said he'd been adding me on Facebook but I'd always decline his requests. But that was my mom controlling my account. After we reunited, he showed me emails he'd sent trying to contact me.

What happened next?

We chitchatted online for a few days and found out we were similar. We shared the same favorite TV shows — The Simpsons and The Big Bang Theory — and we both love to draw. He came to see me about a week later. You wouldn't have believed we hadn't been around each other for 12 years. The idea of "getting to know him" seemed strange because we are so much alike. He came and hung out all day and then I asked to come spend a week with him — he lived in a small town about 30 minutes away. I think my mom knew I was going to move out and it really was getting to the point where I needed to escape, she was so controlling.

So can you remember what it was like the moment you and your dad were reunited? Was there an instant attraction?

It was so weird and confusing. I was seeing my dad for the first time in forever but it was also like, He's so good-looking! And then I was like, What the hell are you thinking? What is wrong with you? I saw him as my dad but then also part of me was like, I'm meeting this guy who I have been talking to over the internet and really connecting with and I find him attractive.

Was there a single moment you realized that you were sexually and romantically attracted to your dad?

After I had stayed with him for about five days.

What happened?

He was living with his girlfriend. On the first night he slept on the couch and I slept on the floor, just to make sure that I was okay.

Why was that?

Sleeping in new places makes me very anxious so I asked him to stay with me in case I had one of the terrible nightmares I usually experience. The second night I had him sleep on the couch again and then the third night I fell asleep with him on the floor lying on his chest, in his arms. The fourth night rolled around and we ended up on the floor again. This time we actually cuddled. When he woke up, we were spooning. I didn't know this at the time but later, after we admitted our feelings, he told me he had had "morning wood" and had gone to fix it.

Do you mean he went to masturbate?

No, he just went to pee. He didn't want me to see that he had an erection. Later that day, we went shopping because I had grown out of all my shorts, so I asked him if he could buy me some new ones. I was trying them on and asked him how I looked and he said I looked good and I felt like I was picking up on something more, but I pushed it out of my head. That night we were play-wrestling in the room I was going to sleep in and I bit him. He was wearing a pair of basketball shorts and a tank top and after I bit him I could see goose bumps pop up from his toes to his shoulders. Then he pinched my inner thigh and I got goose bumps.

We stopped and said that we didn't know what was going on but admitted that we had strong feelings for each other. We discussed whether it was wrong and then we kissed. And then we made out, and then we made love for the first time. That was when I lost my virginity.

Did you tell him you were a virgin?

Yes. I told him I wanted him to be the first person I made love to. We talked about how it could be awkward if it didn't end up working out. He also said that if I didn't feel comfortable at any point I should tell him.

What was it like?

There's a reason I lost my virginity to him — because I'd never felt comfortable with any other man. It was insanely sensual. It lasted for about an hour and there was a lot of foreplay. We both had orgasms. We are so similar, so it's so easy to sexually please each other. For example, we both love neck-biting. I've never been in a more passionate, loving, fulfilling situation.

Even the first time, because often it's not the best sexual experience …

That's what I said! I'd heard that it would hurt so I was expecting pain, but we were both so careful with each other. I think it was also a good experience because most guys my age are only interested in having sex with you. I could tell that wasn't the case with him.

What was it like afterward?

It wasn't weird at all. It felt so natural. It didn't even feel taboo. I felt like I had just made love with a man who I'd been with for years.

Is the father-daughter dynamic part of your sex life?

Not usually, but it has come up a couple of times when one of us blurts out "baby girl" or "daddy" or something. Last time it happened, we both stood up and stopped doing what we were doing. It caught us off guard.

How quickly did he end things with his girlfriend?

We made sure to move out of the girlfriend's immediately because we knew we couldn't be together there. Before her, he was with a woman for eight years and she's now our roommate. Talk about awkward for the first three months!

Did you tell her about the nature of your relationship?

She found out when she heard us making love. I guess we didn't realize how thin the bedroom floor was. She really didn't mind. Now we're like a little family. She calls me her daughter.

You're engaged?

I'm planning on a full-on wedding but it won't be legally registered. And personally, I don't believe you need a piece of paper to prove that you want to be with the person you love. When you get married, you are signing part of yourself over to somebody. We'll tell everybody that we got our marriage license, but they don't have to see it. One of our friends will act as the celebrant.

Will you have a wedding? Do you have it planned?

Yes. I want it to represent our uniqueness, so we aren't doing a white wedding. The color scheme is black and purple, and we are both going to wear Converse tennis shoes. He's wearing jeans and a nice dress shirt. He says he's not wearing a bow tie, but it's my wedding and I am saying that he is. My best friend will be my maid of honor and she'll be dressed in purple. My grandmother and grandfather — my fiancé's parents — are going to attend and my grandpa will give me away. The tables will have bouquets of trees without leaves to represent our marriage, which will be like a growing tree. My dress will be black.

Do you worry about the potential genetic problems associated with having kids with your biological father?

Nope. I wouldn't risk having a kid if I thought it would be harmful. I've done my research. Everybody thinks that kids born in incestuous relationships will definitely have genetic problems, but that's not true. That happens when there's years of inbreeding, like with the royal family. Incest has been around as long as humans have. Everybody just needs to deal with it as long as nobody is getting hurt or getting pressured or forced.

There are so many people having kids who will be passing on health problems, people with diabetes or mental health issues, or AIDS. My mom was allowed to have kids and both her and her mom were bipolar. My research tells me that the only real genetic risk is high blood pressure, which is controllable.

Were you ever sexually abused when you were younger?

No, and my dad has told me that the thought of being involved with me when I was little is appalling to him. Once when I was about 4 I was in a golf cart with my great-great grandma's husband and he touched me on my inner leg. It wasn't super-aggressive, but I felt very uncomfortable about it. I told my father and he called my mom and they took me to a children's hospital to get examined. There were no signs of abuse.

The interview can be read in full here.

It is thought that GSA can not only occur because the other person might look, act or talk like you; but also because, having missed out on growing up with their relative, they will have forgone the 'Westermarck Effect', which naturally creates a feeling of sexual repulsion towards family members in order to prevent incest and therefore inbreeding.

Catriona Harvey-Jenner Digital Features Editor Cat is Cosmopolitan UK's features editor covering women's issues, health and current affairs.

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