They include details of her campaign against arms dealers and her growing paranoia about potential threats to her life.
For five years the princess talked to psychic healer Simone Simmons regularly, sometimes for hours.
Diana revealed her hopes, plans and troubled thoughts before being fatally injured in a car crash in Paris on August 31, 1997, aged 36
Simone has now told Radar Online about the secrets her famous friend left behind, many of which were recorded as frantic messages on her answering machine.
In two of the tapes, which were played to the news outlet, Diana said in a hushed voice she had “so much” to tell the healer.
Simone is convinced that Diana was about to go public and name a group of international arms dealers on the morning of the crash.
She also heard that the divorced princess intended to move to America and hoped to buy the Los Angeles home of Oscar-winning actor Julie Andrews.
Contrary to claims made by the billionaire Harrods owner Mohamed Al-Fayed, Diana was not in love with his son Dodi, and never intended to marry him.
Instead, she apparently hoped to reunite with her former partner, the British-Pakistani heart and lung surgeon Hasnat Khan.
Another well-known relationship with British ex-rugby player Will Carling began when Diana asked him to create a personal training programme that would help regain her figure after suffering bouts of the eating disorder bulimia.