The Experiment

Identical twins are beautiful quirks of nature, perfect genetic copies of each other with a bond so close many believe they're telepathic. Understandably, twins, and even rarer identical triplets, have been magnets for curious scientists trying to answer that profound question: Is it nature or nurture that determines who we are? But one well-known psychiatrist in the United States became so obsessed by his research he engineered a truly heartless experiment. He separated sets of identical twins and triplets at birth and studied them as they grew up apart. Incredibly they never even knew their siblings existed. But this doctor's cruelty was finally exposed when decades later – in a one in a million chance – they found each other and discovered an unbelievable truth.

Reporter: Liam Bartlett

Producers: Gareth Harvey, Nick Greenaway