Cardinal Albino Luciani became Pope John Paul I on 26 August 1978. He died unexpectedly 33 days later.
He was discovered in the early morning lying on his bed, a collection of sermons in his hand.
He was considered an excellent communicator, and his warm personality earned him the nickname of "the smiling Pope". But his death shook the Catholic Church.
Rebecca Kesby spoke to Cardinal Beniamino Stella who knew him well.
This programme was first broadcast in 2017.
(Photo: Pope John Paul I. Credit: Getty Images)