Schoolboy, Ritesh, from Garhwa in India, had been living in pain for seven months with stomach ache leaving doctors baffled as to the cause.
Following 12 weeks of upset, the child's parents then admitted him into a private hospital on Thursday, where an ultrasound revealed a knot inside of his stomach.
A team of five surgeons then immediately operated on Ritesh to remove it.
But following the three hour operation, 'stunned' doctors said that the knot was in fact an underdeveloped embryo that had been inside of him since birth.
According to Pradesh18 , the foetus had developed hands, feet and even hair.
Speaking to the Hindustan Times newspaper after the surgery, a senior paediatrician said that the case was one of the "rarest of the rare".
Dr Alok Bhardwaj said: "This is the rarest of rare cases. But the boy's problem was successfully treated. He is completely stable and is recovering fast. Had it not been removed, it would have caused a severe problem to the boy in the future."
Dr Awadesh Kumar Kaushik, the laparoscopic surgeon at the hospital in Varanasi, said: "It is a developmental abnormality in which a mass of tissue resembling a foetus forms inside the body.
"One theory says that the mass begins as a normal foetus bu becomes enveloped inside its twin."