A 60-year-old man in Nagpur, India, lived for 36 years with an unusually swollen abdomen before doctors discovered the cause was an extremely rare medical condition.

The man, named Sanju Bhagat, was diagnosed with fetus-in-fetu syndrome, meaning a twin fetus was “stuck” inside the other twin’s body while still in the womb. This is considered a form of “vanishing twin syndrome,” where one embryo stops developing during pregnancy but is not completely absorbed by the body.

Because of his unusually large abdomen, Bhagat was often teased and nicknamed “the pregnant man.” However, due to difficult living conditions, he tried to ignore the condition and continue working to earn a living, despite his family’s constant worry.

It wasn’t until 1999, when the bulge in his abdomen began pressing on his diaphragm, causing him difficulty breathing, that Bhagat was taken to a Mumbai hospital for examination.

Initially, surgeon Ajay Mehta believed the patient had a large abdominal tumor. However, during surgery, an unexpected situation arose. The doctors opened his abdomen and prepared to remove the tumor. Instead of the cancerous mass they suspected, they discovered the body parts of a fetus inside.

“He put his hand inside and said there were a lot of bones,” a doctor recounted, according to History Defined.

“First a limb appeared, then another. Then parts of the genitals, hair, jaw, and many other body parts.”

The team of doctors said they were both horrified and bewildered by this discovery. One member of the team even described feeling like he was “shaking hands with someone else” inside the patient’s abdomen when touching the internal structure.

According to the U.S. National Library of Medicine, fetus in fetu is an extremely rare condition in which a malformed fetus is located inside the body of its twin.

In a meta-analysis, Hopkins et al.’s team reported fewer than 100 cases in the medical literature worldwide.

Scientists believe this phenomenon occurs when the twins’ development is disrupted very early in pregnancy. One embryo stops developing and becomes “encased” within the other, continuing to exist as a parasitic structure.

However, the exact mechanism of this syndrome is still not fully understood. Experts also noted the need to differentiate between fetus in fetu and teratoma, a type of tumor that can contain hair, teeth, or body tissue.

Bhagat’s case is considered one of the most astonishing examples of this rare syndrome, as the man lived for over 30 years without knowing he had an undeveloped “twin” inside him.