"Diana, 7 days" recounts the events following Diana's death 20 years ago. She was killed with her lover Dodi al-Fayed when their limousine crashed in a tunnel in the French capital Paris as it sped away from pursuing paparazzi.
Her children, Princes William and Harry, who were aged 15 and 12 when she died, spoke about her death for the first time in another documentary aired in July, but neither mentioned the role of their father during the 90-minute programme.
"He was there for us," Prince Harry told the BBC, of the heir to the throne. "One of the hardest things for a parent to have to do is to tell your children that your other parent has died."
Following Diana's death, the royal family was subject to public criticism for its perceived treatment of the princess, who had struggled to fit into the monarchy and deal with her husband's infidelity.
Some questioned the wisdom of having the young princes walk behind their mother's coffin as it processed through London past vast crowds of mourners.
Diana's brother, Earl Spencer, described it as a "bizarre and cruel" decision, and Prince Harry told U.S. magazine Newsweek in June that no child should be expected to do that "under any circumstances".
Prince William, who described using his fringe as a "safety blanket" throughout the "very long, lonely walk", said it was their duty to take part and that the decision had been "collective".
The prince also defended Queen Elizabeth's much-criticised decision to keep the family at a remote Scottish castle in the aftermath of Diana's death, saying it had given them the "privacy to mourn".
"Diana, 7 Days" will air on Sunday at 7:30 p.m. (1830 GMT).
(Reporting by Emma Rumney; Editing by Robin Pomeroy)
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)