“This is the first time that the two of us have ever spoken about her as a mother,” says Prince Harry in a new teaser for “Diana, Our Mother: Her Life and Legacy.” He and his brother, Prince William, are discussing their very personal takes on Princess Diana.

Born Diana Spencer, Princess Diana broke with standard monarchy protocol by divorcing Prince Charles and speaking publicly about his affair with Camilla Bowles. Famed for her charitable and humanitarian work, Princess Diana fought to raise awareness about landmines, child bereavement, homelessness, and HIV/AIDS. She died in a car crash August 31, 1997 at the age of 36. But it’s Princess Diana’s life — and her warmth — that her sons focus on in the trailer.

“She was very informal — and really enjoyed laughter and fun,” Prince William observes. Harry adds, “She was one of the naughtiest parents.” Both seem to recognize some of the negative stereotypes associated with royal life: humorlessness, oppressive formality, and oblivious privilege. But according to the Princes’ accounts, their mother was nothing like that. “She understood that there was a real life outside of the palace walls,” William emphasizes.

Directed by Ashley Gething (“Our Queen at Ninety”), “Diana, Our Mother: Her Life and Legacy” will be broadcast on HBO sometime in July — an exact premiere date hasn’t been announced yet — and will feature new archival material and commentary from many influential figures in the Princess’ life.

ABC will air a docuseries about Princess Diana in August. Her story has also been told in narrative works, including 2013’s “Diana,” which sees Naomi Watts portraying the last two years of Princess Diana’s life and her romance with Hasnat Khan.

Check out the teaser to hear more about Diana from those her knew her best.