MEGHAN and Harry "betrayed the Megxit deal and have caused everlasting damage to the Royals," Tom Bower has blasted.
Royal biographer Bower said the Sussexes have used their royal titles to get publicity despite saying they just wanted privacy.
Speaking on The Sun's Royal Exclusive show, he said Harry and Meghan have been "treacherous and disloyal".
Bower said: "They betrayed and ignored the agreement that they settled on.
"Allegedly they were going to California for privacy and to leave the royal family. They've done the exact opposite."
Bower also said the Sussexes aim to "profit from their notoriety" - and the royals should have seen it coming.
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He said: "I think Meghan and Harry have had a hugely negative impact on the royal family - the damage has been everlasting.
"The tragedy is that they tried terribly hard to help Meghan. After all, Charles escorted her into the wedding in St. George's Chapel.
"The Queen assigned over half a dozen people to look after Meghan and help her get into the ways of the royal family.
"But they could never win. We now know in hindsight that Meghan never really intended to stay.
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"The guest list for her wedding showed her real ambition was to be a star in California.
"Harry's friends were excluded from the guest list for the dinner in the evening."
Bower added: "So we know the agenda was something which the royal family could never really get to grips with.
"That's why their reaction when the assault came through the Oprah Winfrey and Netflix interviews was lame and self-defeating.
"They should have been far more aggressive in their response to assert their own credibility.
"After that came the publication of Harry's autobiography Spare, which peddled even more lies and trouble.
"It was a worldwide bestseller, because the world was fascinated that two royals could be so treacherous and disloyal.
"They'd never had that in their lifetimes before. There's waning interest in them now.
"People are beginning to see the truths which I exposed two or three years ago in my book Revenge.
"The truth is that they are narcissistic and intent on self-glorification to profit from their notoriety."
Bower said: "At the time, no one wanted to believe it could be that bad."
The royal biographer also branded Prince Andrew's last public outing a "catastrophic mistake".
In February this year, the Duke of York was among a number of royals who attended St George's Chapel in Windsor Castle for the Thanksgiving service held in honour of Greece’s late King Constantine.
Andrew was seen beaming as he led the way in a rare public appearance as mourners arrived for the service.
Queen Camilla arrived separately meaning that the Duke of York stepped forward to usher in more minor royals including Princess Anne, her daughter Zara and husband Mike Tindall.
His ex-wife Sarah Ferguson was by his side as they marched into St George's Chapel.
Bower said: "Andrew should be invisible. I blame the King for not being more authoritarian.
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"Charles should have ordered Prince Andrew to stay out of public view."
"That memorial service front row was catastrophic mistake - Andrew pushed himself to the front."
Megxit timeline
- November 2016 - Harry formally reveals he is in a relationship with Suits actress Meghan Markle.
- September 2017 - Meghan tells Vanity Fair the couple are in love and happy together.
- September 2017 - The couple make their first public appearance together holding hands at the Invictus Games in Toronto.
- November 2017 - Prince Charles issues a statement revealing Harry and Meghan are engaged.
- May 2018 - Harry and Meghan tie the knot, becoming Duke and Duchess of Sussex.
- October 2018 - The couple announce they are expecting their first child while on their first overseas tour in Australia.
- March 2019 - Harry and Meghan set up their own household, splitting their joint operation with Prince William and Kate.
- May 2019 - Meghan gives birth to a baby boy named Archie.
- October 2019 - Harry reveals his rift with his brother William in a bombshell documentary.
- January 2020 - The couple stun the Queen by announcing plans to quit senior roles and settle in North America. After ten days of talks at Sandringham, it's agreed the couple will no longer be working royals and will give up their "Royal Highness" titles.
- March 2020 - Harry and Meghan carry out their last official engagement and move to California.
- September 2020 - Netflix announces a huge deal with the couple.
- February 2021 - Buckingham Palace announces the couple's split as working members of the monarchy is permanent and they will lose their royal patronages.
- March 2021 - The palace says it is "very concerned" about allegations of bullying made by former staff of Harry and Meghan, launching a probe.
- March 2021 - Meghan tells Oprah Winfrey Archie wasn’t made a prince after “concerns and conversations” about “how dark” his skin would be when he was born. She claims Kate "hurt her feelings" and made her cry before her wedding. Harry says Charles has stopped taking his calls and he has been "cut off" financially.
- January 2023 - Harry publishes his tell-all memoir Spare, launching scathing attacks on William, Kate and Camilla. He says he and William once got into a physical fight over Meghan.
- April 2023 - Harry has a "heart-to-heart" talk with his dad before agreeing to come to the Coronation in London.
- September 2023 - Harry rejects an offer to spend the anniversary of the Queen’s death at Balmoral with his father.
- February 2024 - Prince Harry flies to the UK to be with his father as royal experts claim their four-year rift could be put aside. They meet for half an hour before Harry flies home. He does not meet William.