Born in Barbados in 1963, they moved to Haverfordwest in Wales shortly afterwards when their parents emigrated in search of work. Even at an early age they appeared unusually close - even for twins - and took to speaking in a rapid Creole dialect that others were unable to comprehend. Indeed, some believed that they were using an invented shared language, which is sometimes seen in twins or close siblings during their early years. Only by recording their speech and slowing it down were researchers able to establish that they were speaking heavily inflected English, with emphases and stresses in unusual places to further obfuscate their words.
As the only black girls, they were also routinely subject to racism and bullying, which served to make them withdraw into their own isolated world, eventually only speaking to one another and refusing to make conversation with anyone else apart from Rosie - their younger sister. Later, June revealed that the pair made a conscious pact to never speak to anyone else.
So isolated had the pair become that at 14, therapists recommended that they be separated to force them to communicate with other people, and they were sent to different boarding schools. Instead of opening up to the experience, both girls became even further withdrawn without each other, becoming almost catatonic.
After the moved back home together, they began to augment their isolated existence through elaborate storytelling: play-acting through dolls, but expanding to create plays and soap operas for them, which they would act out on tape for their little sister.
In 1979, they received diaries for Christmas - which would become more significant as the years passed. The act of writing seemed to inspire them, and they subscribed to a creative writing course, soon displaying an aptitude for fiction. Through a self-publishing house, they actually published several novels - all of which had bizarre scenarios.
As an example, Jennifer's work The Pugilist is about a doctor whose child is dying of a heart condition. In a desperate bid to save his life, the doctor kills the family dog and transplants its heart into his son's body, only for the dog's spirit to possess his son and make seek revenge.
Following a brief fling with boys from a US Army base and minor experiment with drink, the girls began to commit a string of minor criminal acts - including arson. Their "crime spree" lasted five weeks, and saw them convicted of 16 separate offences.
This brush with criminality, coupled with their bizarre shared existence saw them committed to Broadmoor Hospital for "treatment". At just 19, they were the youngest patients, and found themselves amidst a population of mainly much older - and often violently criminal - men. It would be 11 troubled, wasted years before they were allowed out.
The pair were given doses of antipsychotic medications to no avail. The main effect was to render them unable to concentrate. Although they filled their diaries with copious writing, it was mainly concerned with their own inner lives and feelings and displayed none of their previous taste for fiction.
Over their long years of confinement, their feelings towards each other veered often towards hatred - each feeling trapped by their relationship to the extent that they began to believe that neither of them could be freed from their shared silence until one of them was dead.
So pervasive was this belief, that the twins discussed which of them should die - even as it became clear that they were going to be discharged from Broadmoor after 11 long years. Eventually Jennifer agreed to die, as she was the oldest of the two.
In May 1993, they were finally discharged from the hospital, but their tale still held one fascinated, bizarre and tragic twist. In the van taking them back to a clinic prior to discharge, Jennifer began to complain of feeling unwell - her speech becoming slurred and appearing to be sleeping with her eyes open, her head resting on her sister's lap.
On arrival however, she was found to be completely unresponsive, and was rushed to hospital. That same day she died from acute myocarditis.
Although myocarditis can result from many environmental or underlying health complications, no discernable cause for the onset of the condition was ever found. June believed that Jennifer's death was conscious, and that she had died so that June herself could be freed from the self-imposed pact the twins had made.
Following a handful of interviews with curious members of the press, June sought anonymity and returned to Haverfordwest, where she continues to live with her family.