Doctors found a dead foetus, complete with hands, legs, nails and a partially formed head, in the stomach of a four-year-old boy.
The boy, from Midnapore district in India's eastern state of West Bengal, had complained of a stomach ache which doctors feared could be a tumour, the International Business Times (IBT) reported.
But when they investigated with a scan, they found the foetus - thought to be his twin that had attached itself to his body in utero - and removed it after a long operation.
The phenomenon, known as 'foetus in foetu' (baby within a baby) occurs in just one in every 500,000 to 600,000 people.
Dr Shirshendu Giri, who performed the surgery said: "The dead embryo which had hands, legs, nails and a partially formed head was removed from the child's body after a long operation. The boy is is alright now still under close observation."
During early stages of a twin pregnancy, one foetus can enter the other through the umbilical cord and become a parasite on its host.
After the birth it becomes an abdominal mass but can have health implications to the surviving baby.
Another case was reported in 1999 when Sanju Bhagat from Nagpur, India was found to have carried his twin for 36 years.