Transcript for Looking back on Princess Diana's final hours

Next to princess Diana who died 20 years ago this summer. Tonight, we're learning more about Diana's final hours with her boyfriend. Martin Bashir takes a look back. Reporter: The summer was nearly over and, according to the friend she telephoned, Diana was anxious to go home and see her sons, but dod wanted one last weekend in Paris. She rang me and said, dodi wants to go to Paris. Would you tell William and Harry at balmoral that I'll be back the day after. Reporter: The Paparazzi were hot on their trail. It was open season on her because she was the most photographed. Everybody could sell pictures of her. Everybody wanted them. Reporter: Some time after midnight, the couple made a fateful decision to return to dodi's apartment. They would leave by the Ritz's rear exit, which was reached by going through the hotel kitchen. Back in London, the other man in Diana's life was urgently trying to reach her. Hasnat khan, a british/pakistani heart surgeon she called "Mr. Wonderful." It's tragic to think that on that last night, as Diana was preparing to get into the car that would take her into the ALMA tunnel to her death, that hasnat khan was trying to reach her on the phone. Does the world realize that her romance with dodi Al fayed was only 30 days from beginning to end? Not two years, as was the one with hasnat. Hasnat khan was the love of her life. Special correspondent martin Bashir looking back. He'll have much on two-hour primetime documentary special right here tomorrow night at 9:00 eastern.

This transcript has been automatically generated and may not be 100% accurate.