The 60-year-old man - who has declined to give his name - was raised reliant on hand-outs from the state after the man he thought was his father died when he was just two. The woman he considered his mother had to support his three older brothers and there were few comforts in their one-room apartment as he grew up.
The man had to study at night-school while working day shifts in a factory before finding steady employments as a driver with a transport company. He never married and helps take care of three men who are not his brothers, including one who has suffered a stroke.
Meanwhile, the infant that was given to the man’s biological parents was born 13 minutes later at the San-Ikukai Hospital, in Tokyo’s Sumida Ward, and grew up in relative affluence.
The boy had a personal tutor, went to university and is the head of a successful real estate company. His three other brothers work for major companies, according to media reports.
Questions were only raised when the three brothers of the man who was given to the wealthy family recently realized that he bore little resemblance to any of his relatives.
In 2011, the family requested access to hospital records and DNA tests subsequently confirmed the mistake.
The error apparently happened when a midwife took the new-born babies away to be bathed and then returned them to the wrong mothers.
Speaking to media in Tokyo, the man condemned to a life of hardship described his shock at learning the people he grew up believing to be his parents and brothers were unrelated to him.
“I wondered how on earth this could have happened,” he said. “I could not believe it. To be honest, I did not want to accept it.”
The Tokyo District Court on Tuesday ordered the hospital to pay the man Y38 million (£227,346) in damages as a result of the mix-up, significantly less than the Y250 million (£1.5 million) the plaintiffs had been seeking.
“The links between the man and his real parents were severed and the man was forced to grow up in a poor home,” Judge Masatoshi Miyasaka said in his ruling. “The mental anguish he went through was enormous.
“There were far-reaching differences between the two family environments and the plaintiff suffered an unreasonable loss as a result,” the ruling said.
“It is impossible to assess the scale of the pain and disappointment both the parents and the man had to suffer, as they were deprived of opportunities to enjoy their parent-child relationship for ever.”
The man’s biological parents both died before the error came to light and he is still coming to terms with the impact of the events of 60 years ago.
“I might have had a different life,” he said.
“I want [the hospital] to roll back the clock to the day that I was born.”
He is particularly angry at never having the opportunity to meet his real parents.
“As I saw picture of my parents, I wanted to see them alive,” he said. “For months, I could not hold back the tears every time I saw their pictures.”
He added that the woman who raised him as her son may have suspected that something was amiss.
“I think my foster mother may have sensed it,” he admitted, pointing to the physical differences between himself and his brothers.
The man who grew up impoverished would have been the oldest son in the family had he come home with his biological parents, leaving a question mark over the position of the man who took his place if he took over the family business, as is often the case in Japanese families.
His three real brothers, who insisted that the DNA test be carried out on the man they grew up believing was their oldest brother, have told their biological brother that they want to build a relationship and make up for the years they have lost.
"I was happy to hear that and it's what I want to do," the man said.
The hospital initially attempted to have the case dismissed on the grounds that the 10-year statute of limitations had run out. The court dismissed that claim and ruled that the statute of limitations only began when the results of the DNA tests were confirmed.
The hospital has not confirmed whether it will appeal the ruling.
BA/BA