Prince Harry and Meghan Markle’s interview with Oprah could include a "fierce attack" on palace courtiers and damage their relationship with the royals, an expert has argued.

The chat with the legendary US chatshow host is set to be broadcast on CBS on Sunday, March 7 at 8pm EST [1am GMT].

It was originally scheduled to run for 90 minutes but has since been extended to two hours.

The network released a teaser trailer on Sunday, February 28, in which Oprah asks Meghan: "Were you silent, or were you silenced?"

Royal expert Richard Fitzwilliams believes the interview could seriously affect their ties with The Firm.

Prince Harry and Meghan Markle hold hands during a teaser trailer for their Oprah Winfrey interview
A teaser trailer has offered viewers a glimpse of Prince Harry and Meghan Markle's interview with Oprah Winfrey

He told the Daily Star: "We will see when it airs, but the audience in a no holds barred interview - which this claims to be - will primarily want to know why they stepped back and then down as working royals."

Mr Fitzwilliams continued: "We know there will be fierce attacks on media intrusion and probably on courtiers.

"How personal will it get? How sensational? Something as big as this will affect their relationship with the rest of the Royal Family for the foreseeable future."

Oprah Winfrey during her interview with Prince Harry and Meghan Markle
The chat with the legendary US TV host will be broadcast on March 7

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In the interview, Harry and Meghan are expected to discuss Megxit at length and their various charity projects.

The Duchess of Sussex and Oprah are good friends, and the US TV host is thought to have helped her and Harry find a place to stay when they arrived in Los Angeles.

Mr Fitzwilliams added: "I don’t think that it is a good idea for members of the Royal Family to do a no holds barred interview about what life was like when they were working royals.

"I mean, it’s the principle of it."

Days after the interview was announced, Buckingham Palace announced that Harry and Meghan would not be returning as working royals.

They were also stripped of their remaining patronages and honorary titles.

Harry lost the following military titles – Captain General of the Royal Marines, Honorary Air Force Commandant of the Royal Air Force Bas Honington, and honorary Commodore-in-Chief of the Royal Navy’s Small Ships and Diving Operations.

Prince Harry and Meghan Markle hold hands during a teaser trailer for their Oprah Winfrey interview
The running time has been extended to two hours

Meanwhile, Meghan lost her patronage of the National Theatre The Association of Commonwealth Universities.

Recent reports even suggested Prince Charles had stopped paying for Harry and Meghan's mail service at Clarence House.

It forms part of the Megxit review, according to the Daily Telegraph.

In the recent CBS teaser, Harry also appeared to offer a thinly-veiled dig at his dad.

He said he "can’t begin to imagine" what it would have been like for his late mum, Princess Diana, who "went through this process by herself" all those years ago.