Senior editor, style

Prince Harry of Wales and Prince William, Duke of Cambridge, discuss their late mother in the HBO documentary “Diana, Our Mother: Her Life and Legacy.” (HBO)

“They always live with you, people you lose like that,” muses Prince William, the 35-year-old Duke of Cambridge and future king of England, whose mother, Diana, was killed in a Paris car crash 20 years ago next month. “My mother lives with me every day.”

HBO’s hour-long documentary, “Diana, Our Mother: Her Life and Legacy” (airing Monday night) offers this rare conversation with Diana’s sons, William and his brother Harry, 32, who get out their mother’s old photo albums and use the opportunity, as they must, to promote some of her favorite charities and causes. The film, which was directed by Ashley Gething and kept under wraps by HBO, is a brisk and polite review of Diana’s life, the way some of her closest friends, employees and relatives remember it, including her 1981 marriage to Prince Charles, their separation in 1992 and divorce in 1996.

A month ahead of an onslaught of anniversary coverage that includes at least half a dozen TV specials, “Diana, Our Mother” is probably all we’ll hear from William and Harry this time around, and, to be entirely honest, it feels like just enough. Just enough of the anguish. Just enough review of her good works (visiting AIDS patients when no one else would, campaigning against land mines). Just enough rumination on her phenomenal wattage.

Princess Diana carries Prince Harry on her shoulders. (Tim Graham/Getty Images)

It’s too easy to turn the story of Diana — and her death especially — into a gruesome set of conspiracy theories or a sappy, never-ending wallow. At some point, we really do have to let go and let it become history. “Diana, Our Mother” is a coordinated attempt to once more try to head the wolves off at the pass. Then and now, it’s an impossible task.

Time has worked some of its kindnesses, however. Held to the even harsher light of the 21st-century mediasphere, the pictures and footage of Diana in her prime seem like valued artifacts from 100 years ago, safely keeping her in another era’s definition of superstardom. There are still trouble spots to be considered: her give-and-take relationship with the media and the paparazzi that hounded her to the moment she died, and the fickle public that could never get enough of her. There is something yet to learn about her influence on the royal family, which is still deeply felt.

And what of her sons, who, at 15 and 12, so stoically walked behind her casket and then put away nearly all public expressions of their grief? How do they think of her now? What do they remember? They remember her as their mum.

William is more circumspect in the film, recalling Diana’s principles and approach to her duty more than the private moments they shared (aside from the embarrassing time his mother invited a trio of famous supermodels to visit him on his birthday).

“She understood there was a real life outside the palace walls,” William says. “She wanted us to see it from a very young age.” She took the boys with her to homeless shelters, one of which William still regularly visits.

Harry, who says he has only cried once since his mother died and thinks he still has grief issues to work through (“There’s a lot of [it] that still needs to be let out”), has memories that are more emotional and tied to specific moments: Her laughter. Her driving her car with the top down and Enya songs blaring.

Diana, Harry and William ride a log flume at Thorpe Park. (Julian Parker/UK Press via Getty Images)

“Our mother was a total kid, through and through,” Harry says. “One of her mottos to me [was] ‘You can be as naughty as you want — just don’t get caught.’ ”

Both men remember the last phone call from her, some hours before she died. They were spending the summer with their father and grandmother, Queen Elizabeth, in Scotland; when Diana called, they were eager to get back outside and gave her short shrift. Harry says he will regret that fleeting moment “for the rest of my life, how short that phone call was.”

“Diana, Our Mother” also seems to be a chance for William and Harry to subtly transmit to Diana that everything turned out okay. She’d be 56 now, probably doting on her two grandchildren. The brothers don’t shy away from imagining it, but they don’t elaborate on it either.

Her legacy to her sons — and perhaps to all of us who are so busy sharing intimate details on social networks — is to be careful about how much you give away. A little, not a lot. While managing to elide most of Diana’s more unseemly entanglements with the media, the film includes one of the most memorable clips that exists of her; the time she took William and Harry on a ski holiday in Austria. She is seen walking up to a camera scrum and blocking a video lens with her hand, begging the photographers to leave her and her sons alone. It’s still heartbreaking to watch, and it has left William, especially, with a lot to say on the subject.

“I think it was an industry that lost its way quite heavily,” William says. “Lost its sense of dignity, lost its perspective on what was appropriate.”

The only times he remembers his mother crying, he adds, had something to do with the media. “Harry and I lived through that, and one lesson I’ve learned is you never let [the media] in too far, because it’s very difficult to get them back out again. You’ve got to maintain a barrier and a boundary, because if both sides cross it, a lot of pain can come from it.”

Diana, Our Mother: Her Life and Legacy (65 minutes) airs Monday at 10 p.m. on HBO.