Stanford University, 1971. One of history's most notorious psychology studies begins. Led by Dr. Philip Zimbardo, the experiment simulated a prison environment and assigned students to the roles of guards and prisoners. Myths abound about what really happened but in this documentary series, participants take a seat in front of the camera to reveal never-before-heard details of an event that has shaped our understanding of human nature and good versus evil for the past 50 years. Watch The Stanfor

At Stanford University in 1971, one of history's most notorious psychology studies took place. The experiment simulated a prison environment and assigned students to the roles of guards and prisoners. Hear from participants in this gripping documentary series, about what really happened. Watch The Stanford Prison Experiment: Unlocking The Truth on Sunday 15th June at 9pm, on #NationalGeographic UK. | National Geographic UK