Since she was less than a year old, the unnamed girl has allegedly been locked away in her grandparents' house in Attendorn, a town just east of Cologne, Germany.
According to welfare officials, the child can read and do maths, but she is so physically underdeveloped that she struggles with day-to-day tasks, such as climbing the stairs or navigating uneven ground.
The young girl's mother had falsely told authorities that they had moved to Italy.
Her father, who was already separated from her mother at the time of her birth, told German newspaper SauerlandKurier that he found a note on his car windscreen when the child was just six months old, telling him that they had moved to south-west Italy.
The biological father claims he contacted welfare authorities back in 2015 when he repeatedly spotted the mother and child in Attendorn, but when authorities questioned the maternal grandparents, they confirmed the mother's story.
The father also claimed that he grew more suspicious when he sent gifts and letters to his daughter in Italy, but they all came back unopened.
But earlier this year, investigations launched after police received a tip-off about a rumour that the child had been locked away in her grandparents' house for years.
After learning that the mother and child had never lived in the Italian address they had listed, welfare officers and police got a court order to search the grandparents' home and discovered the girl.
Now, officials are working to determine what happened, as the mother and grandparents remain silent.
The girl has been placed with an emergency foster family while police investigate further.
There is reportedly no evidence of physical abuse of malnourishment, according to doctors who examined the child after she was freed on 23 September.
However, prosecutors understand that this little girl had never seen the outside world, been to school, or been in contact with another person.
A spokesperson from the national Child Protection Association told German media: "The world is now upside down for the child. It will feel like being on another planet."
Authorities are reportedly giving the young girl some space and time to process her new surroundings before they begin questioning.
The mother and grandparents are being investigated on suspicion of false imprisonment and mistreatment of a minor.
Prosecutors have suggested that the mother could face up to ten years in prison.
Topics: News, World News, Crime, Germany
