Britain’s royal family on Sunday braced for further revelations from Prince Harry and his American wife, Meghan, as a week of transatlantic claim and counter-claim reaches a climax with the broadcast of their interview with Oprah Winfrey.

The two-hour chat with the US chatshow queen is the biggest royal interview since Harry’s mother Princess Diana detailed her crumbling marriage to his father Prince Charles in 1995.

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Diana’s shock admission of affairs on both sides, and her life in the world’s most famous family, was watched by more than 22 million people in Britain — a record.

But that could be eclipsed by Harry and Meghan’s tell-all with Winfrey, who has reportedly sold it to US broadcaster CBS for $7-9 million (£5.1 million to £6.5 million, 5.9 million to 7.6 million euros).

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Winfrey also retains the international rights, which will feed an appetite of interest about Britain’s centuries-old monarchy — and their troubles — across the globe.

“Tin hats on,” one royal aide was quoted as telling the Sunday Times, after a drip of excerpts in which Meghan complained about the strictures of royal life from her gated Californian mansion.

Viewers will tune in to see if she and Harry have scores to settle with Buckingham Palace since leaving the royal frontline — and if so, how far will they go?

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Close attention will be paid to any suggestion by Meghan, who is mixed race, that racism played a part in their shock decision to move to North America.

The former television actress, 39, has been portrayed in some British newspapers as headstrong, calculating and spoiled, and the couple reckless and selfish for quitting royal life.

But in her defence, Meghan’s supporters, particularly in the United States, have seen hints of racism, claiming the monarchy could not deal with a “strong black woman”.

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In one excerpt, Meghan, who is pregnant with the couple’s second child, accused the royals of orchestrating a calculated smear campaign and “perpetuating falsehoods” about them.

That came hours after revelations she was facing an internal palace investigation into claims that she bullied royal household staff after she and Harry married in a fairytale wedding in 2018.

Further reports the couple are facing a probe into their charitable foundation have been seen as a counter-offensive by the embattled royals in a bitter battle for public support and sympathy.

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Just hours before the broadcast, Harry’s grandmother, Queen Elizabeth II, and other senior royals, including his father and older brother William, make their own TV appearance.

The Commonwealth Day celebration normally passes with little fanfare in Britain, but this year is being watched closely for signs of implied criticism of Harry and Meghan.

Excerpts released Saturday showed William and his wife Kate — with whom Harry and Meghan have reportedly fallen out — praising global health workers for their work during the coronavirus pandemic.

That is likely to be viewed in British newspapers in contrast to Harry and Meghan, who have been criticised for complaining about their life, even after signing lucrative deals in the last year.

The couple, known formally as the Duke and Duchess of Sussex, are likely to get more public sympathy — and a greater profile — in the United States.

But royal author Penny Junor said the whole affair was “a mess”. “I don’t think there are going to be any winners in it,” she said.

The Sunday Times said the queen, 94, would not watch the interview, which is due to air in full on Sunday night in the United States and Monday night in Britain.

The weekly quoted unnamed courtiers as calling the situation a “circus”, and the palace would “come out swinging” if individuals are attacked.

Viewers will also watch to see if Harry sheds light on his rift with William, after reports he and his wife Kate were lukewarm towards Meghan.

They are also likely to expand on their attitudes to the media, which they said prompted their departure, and against whom they have launched a slew of legal claims.

“My biggest concern was history repeating itself,” Harry, 36, told Winfrey in one excerpt, referring to his mother’s death in a 1997 Paris car crash as she fled paparazzi photographers.

Harry and Meghan first stepped back from royal duties in March last year. It was confirmed last month they would not return and were stripped of their royal patronages and honorary titles.