“I have never had any sexual experience with someone outside of myself.
I was unaware that I could impregnate myself, but I would never go back even with what I know now.
Essentially, the development that should have taken place in the womb with these children happens around 12 years later.
Then when puberty hits, a large surge of testosterone is triggers the male reproductive organs to grow.
This causes their voices to deepen and the development of a penis.
Now 24, he is physically and biologically male - a process that started when he was seven years old. The rare genetic disorder is caused by a missing enzyme which prevents the production of a type of male sex hormone - dihydro-testosterone - in the womb.
He said: 'I remember I used to wear a little red dress. All babies in the womb, whether male or female, have internal glands known as gonads and a small bump between their legs called a tubercle.
Typically, they will possess male sex organs, but these will often be underdeveloped.
They will also often develop breasts and maintain a high-pitched speaking voice.
The documentary makers meet Johnny, who appeared female at birth and was known as Felicitia.
As a child, he did not have a penis and was brought up as a girl.
In fact, biologists now recognise a host of conditions, both genetic and otherwise, which are labelled under the umbrella term 'intersex' - which replaces older terms such as 'hermaphrodite'.
Intersex people may be genetically female, but physiologically male.
Some will be true hermaphrodites, producing both eggs and sperm.