Indian-born Sohna and Mohna are nine- year-old brothers born with a rare condition that leaves them with two heads and one body.
The Channel 4 documentary The Twins Who Share a Body follows the pair and looks at how they managed to reach their ninth year - most babies born with their condition die shortly after birth.
Sohna and Mohna are dicephalic parapagus conjoined twins - they have four arms and two heads, but share their torso and legs. This condition is thought to affect just one in a million.
Dr Rakesh Chouhan said: "It's still a mystery and we're not 100 per cent sure how these things are happening.
"The most remarkable thing is two brains, single body being controlled separately and still they're a single unit."
The documentary asks how these two boys can live fulfilled lives being in just one body - they have been accepted by the community and they seem to live separate lives.
Each twin controls a different side of the body, once can sleep while the other is awake and they can cheat off one another in school.
Their nanny, Parmjit Kaur, said: "Sohna and Mohna think as two separate people. With shoes or socks, Sohna will put on his own and Mohna will put on his own.
"They will never put them on for each other. When they've been playing we tell them to wash their hands and legs.
"Sohna will wash his leg and walk away so we have to take Mohna back so he can wash his leg. That's how it is."
However, Sohna and Mohna's tale is one of unusual success. In Brazil, another pair of dicephalic parapagus twins have been born.
Emanoel and Jesus are currently fighting for survival - with one twin putting pressure on the shared heart and lungs. Doctors are trying to determine if the boys will live the rest of their lives in the same body, or if they could ever be separated, meaning one would be sacrificed.
Around half of all conjoined twins are stillborn. Separation largely depends on where the twins are attached and in many cases, the surgery will result in the death of one or both of the twins.
The first conjoined twins were Chang and Eng Bunker, who were born on 11 May 1811. They were joined at the chest. Both married and fathered 22 children respectively. They died within hours of each other in 1874, at the age of 62.
The Twins Who Share a Body is on 10pm at Channel 4 tonight (Wednesday).