Prince Harry said he 'refused to accept' Princess Diana's death and believed she was still alive until he was 23

• Prince Harry spoke about his memoir, "Spare," in an interview with Anderson Cooper on Sunday.
• He said he couldn't accept that his mother, Princess Diana, died in a car crash in 1997.

Prince Harry said he "couldn't accept" that his mother, Princess Diana, died and believed she was alive until he was 23.

The Duke of Sussex spoke about his upcoming memoir, "Spare," during a"60 minutes" interview with Anderson Cooper Sunday, ahead of the book's worldwide release on Tuesday.

While discussing Princess Diana's funeral, which took place in September 1997, Harry confirmed to Cooper that he had trouble accepting her death and the overwhelming grief that followed.

"I just refused to accept she was gone," Harry said. "Part of, she would never do this to us, but also, part of, maybe this is all part of a plan."

Cooper then asked if Harry believed Princess Diana "decided to disappear for a time," to which he agreed.

"For a time, and then she would call and we would go and join her," Harry said, adding that he out hope for "many years." Cooper added in the interview that Harry told him he believed there was a probability that Princess Diana was alive until he was 23 years old.

In the interview, Harry told Cooper that he didn't accept her death until he visited Paris, France, for the first time. While there, he instructed his driver to travel through the tunnel where his mother died at the exact same speed, 65 miles per hour.

"I wanted to see whether it was possible, driving at the speed that Henry Paul was driving, that you could lose control of a car and plow into a pillar, killing almost everybody in that car," Harry said. "I need to take this journey. I need to ride the same route."