Britain's royals are braced for Netflix's six-part docuseries on Prince Harry and his wife Meghan, after the first extracts reignited a simmering row with his brother William.

Thursday's fly-on-the-wall documentary follows Harry, 38, and Meghan, 41, as their strained relationship with his family unravelled.

It is billed as the couple lifting the lid on what happens "behind closed doors" but risks damaging both the royal family and the couple themselves.

A recent British poll suggested the couple are now the least popular senior royals apart from the disgraced Prince Andrew.

Harry and his brother William, 40, were once close and bonded through their shared grief over the death of their mother Princess Diana.

But they have been at loggerheads since Harry and Meghan, also known as the Duke and Duchess of Sussex, quit royal life and moved to California in 2020.

The couple's complaints about the strictures of royal life -- and even racism in the family -- have made headlines around the world.

One trailer for the programme entitled "Harry & Meghan" shows Meghan looking distressed as Harry throws his head back in apparent despair.

"I had to do everything I could to protect my family," Harry is heard saying.

"No one sees what goes on behind closed doors," he adds.

In the second, released Monday, a lawyer for Meghan, Jenny Afia, claims that during her time in Britain "there was a war against Meghan to suit other people's agendas".

- 'Terrified' -

Diana died in a car crash in Paris in 1997 while trying to shake off paparazzi photographers.

"I was terrified, I didn't want history to repeat itself," says Harry in the latest trailer, referring to the hounding of his mother.

"I realised they (Buckingham Palace) are never going to protect you," adds Meghan, speaking over a clip showing her looking over her shoulder as if fearing she is being followed.

Buckingham Palace refused to comment when contacted by AFP.

British media has been critical of the timing of the first trailer.

Several said it was a blatant attempt to upstage heir to the throne William as he visited the United States and effectively amounted to a "declaration of war".

The Mail on Sunday newspaper last weekend reported that Charles and Queen Consort Camilla were "not worried but wearied" by the constant stream of criticism.

Other sources, however, said they believed the programme would be "worse than the royals imagine" and strained relations could be broken.

"I'm told that it's going to be utterly explosive," one unnamed source told the Daily Mirror.

- Unpopular -

The docuseries airs three months exactly since the death of Harry's grandmother Queen Elizabeth II, and a month before long-awaited publication of Harry's memoirs, "Spare".

Despite their differences with the royal family, the couple attended the queen's state funeral in September.

At one point, William and his wife Catherine appeared to offer an olive branch by inviting Harry and Meghan to join them to view flowers left for the late monarch.

But the two couples were noticeably frosty and hopes for the start of a thaw in relations were dashed further when the warring brothers failed to even make eye contact at the funeral.

A YouGov poll last month indicated that William and his wife Catherine -- also known as the prince and princess of Wales -- were now the most popular members of the royal family.

A total of 81 percent of people questioned had a positive view of William and 75 percent of Catherine.

Only 39 percent of people viewed Harry favourably while the figure for Meghan was 28 percent. Only the disgraced Prince Andrew polled worse.

The Sun tabloid criticised what it called the couple's "obsessive self-pity" at a time of war in Ukraine and a cost of living crisis in the UK.

"The Sussexes plainly despise the royal family. So take their titles," it said, suggesting they be stripped of their royal designations.