Prince Harry is reportedly exploring a documentary to mark the 30th anniversary of Princess Diana's death.

The 42-year-old Duke of Sussex is said to be exploring the possibility of a number of projects to mark the milestone on August 31, which will be 30 years since his mother died aged 36 in a car crash in Paris in 1997.

According to PEOPLE magazine, Harry is considering various ideas including a possible documentary.

It's noted that no documentary project has officially been finalised or confirmed.

However, Harry is said to have reached out to various family members and friends connected to his late mother.

The royal was just 12 years old, and his brother Prince William was 15, when Princess Diana died.

They both spoke candidly about their late mother, and the impact of her death, in 2017 documentary Diana, Our Mother: Her Life and Legacy.

The report comes days after King Charles hit out at Earl Spencer over claims made in his former brother-in-law's new book about the late princess.

Buckingham Palace suggested the 62-year-old earl's grief over his beloved sister had "clouded reason" and "affected judgement" after he claimed in Swan Song: Diana, My Sister that the monarch had sneered Diana would be forgotten "soon enough" during a phone call in the days following her passing.

In a very rare statement, a spokesperson for the king said: "While we do not comment on books as a matter of principle, His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgement and colour memory in ways others do not recognise, even many years after such a loss."

In a preview from the clip serialised by the Daily Mail, the earl wrote in his book: "Prince Charles continued his stream of anger, without me interrupting. Then he stopped.

"I assumed the pause signalled an effort to bring himself under control, but then he unleashed down the phone what I have always taken to be his pent-up contempt for Diana, and his horror that the world was so bowled over by her death. 'Rest assured,' he hissed, 'we'll forget her soon enough!'"

A source close to the king insisted to the Telegraph that the alleged remark was "just not in his nature and it certainly wasn't in his nature at that time, when he was a man absolutely grief-stricken".

Meanwhile, UK indie company Love Monday TV is working on a new Princess Diana documentary including "several hours of intimate" unheard recordings.

Richard Life, SVP Acquisitions and Co-productions for Cineflix Rights, told Deadline in a statement: "What really sets Diana Unheard apart is the unique opportunity to hear several hours of intimate recordings of the Princess; her own story in her own voice at a pivotal point in her life."

Producers of Diana Unheard have accessed secretly taped conversations the late princess had with friend James Colthurst in 1991, which were used for Andrew Morton's book Diana: Her True Story.

Both Colthurst and Morgan, who worked with Love Monday to give them access to several hours of recordings, appear in the series.

Kerene Barefield, Creative Director at Love Monday TV, added: "In making Diana Unheard, we wanted to challenge the narrative that has too often portrayed Diana, Princess of Wales simply as a victim of her circumstances.

"This is Diana not as a passive victim of events, but as a woman taking control of her own narrative and risking everything to make her voice heard.

"Diana Unheard restores authorship of one of the most scrutinised lives in modern history to the woman at its centre."