Omid Scobie has claimed the late Queen liked Kate Middleton because she was 'coachable' unlike 'strong-minded' Princess Diana.
Harry and Meghan's 'cheerleader-in-chief' took aim at The Princess of Wales in his new book Endgame, which has been published in Australia.
In a chapter dedicated to the future Queen, he says her workload is lower than other senior royals, and that she's 'technically a part time working royal'.
He claims she 'does not plan to increase her workload for 10-15 years', or until her children reach adulthood, and added that she earned the nickname 'Katie Keen', because palace press release mitigate her doing less by saying she is 'keen to learn'.
In a clear swipe at the royal, Scobie writes Kate's lifestyle is something most parents could 'only dream of'.
Harry and Meghan's 'cheerleader-in-chief' Omid Scobie took aim at The Princess of Wales in his new book Endgame, which has been published in Australia. Kate is pictured at a recent event
'The late Queen, too, would take off blocks of time throughout the year to recharge, but she was also known to carry out at least three hundred engagements annually.
'Sources said Kate remains "laser focused" on her duty to the family first, and then the Crown.'
Scobie added that Kate also 'often stumbles on her words' when speaking publicly and that she 'didn't want to make' her widely praised Blue Peter performance in June 2019.
Describing it as a 'low-pressure, small-stakes' appearance, Scobie says Kate was 'nervous and "well out of her comfort zone" before the taping'.
He claims a a Kensington Palace source said she 'had never been pushed' until that point.
Scobie today claimed letters between King Charles III and Meghan Markle reveal the names of two people who allegedly commented on Archie's skin colour.
The royal author, whose new book Endgame comes out at midnight tonight, said he could not reveal the identities of the two people for fear of legal reprisals in the UK.
But he said letters were exchanged between Charles and Meghan following the allegation in the Sussexes' bombshell interview with Oprah Winfrey in March 2021.
In an interview with ABC's Good Morning America broadcast today, Mr Scobie was asked whether he knew who made the comments about Archie's skin colour.
Scobie added that Kate also 'often stumbles on her words' when speaking publicly and that she 'didn't want to make' her widely praised Blue Peter performance in June 2019 (pictured)
Royal author Omid Scobie gave an interview broadcast on ABC's Good Morning America today
He said: 'I do know who made the comments about Archie's skin colour. The names were mentioned in letters between Meghan and Charles that were exchanged some time after the Oprah interview.
Omid Scobie's new book Endgame about the Royal Family is set to be released tomorrow
'We know from sources that Charles was horrified that that's how Meghan felt. Those conversations were, and that he wanted to, sort of as a representative for the family, have that conversation with her.
'And it is why I personally think they have been able to move forward with some kind of line of communication afterwards. Though they may not see eye to eye on it.'
Mr Scobie's claims threaten to reignite the 'royal racist' row that came about after Harry and Meghan's interview.
Meghan had alleged in the TV special that an unnamed member of the Royal Family spoke about 'how dark his (Archie's) skin might be when he's born'.
But it is now being claimed that a second member of the extended Royal Household - who may not be a member of the Royal Family itself - also made similar comments.
King Charles III attends St Mary Magdalene Church in Sandringham, Norfolk, yesterday
The two people are not named in Endgame, which is subtitled 'Inside the Royal Family and the Monarchy's Fight for Survival'.
The book makes a series of claims about the royals and looks at its future following the death of Queen Elizabeth II in September last year.
And Mr Scobie added to ABC: 'I think before people assume that I'm calling this the end of the Royal Family, I'm simply declaring that we've reached a sort of pinnacle moment where the royal family as we know it, is at stake.'
He also makes claims about Prince William leaking stories about Harry.
Mr Scobie said: 'He's sharing private information about his brother that ended up on the front page of a newspaper not long later. These are things that have cause irreparable damage in the relations between each other.'
Describing William as a 'company man', he said: 'We have seen the emergence of a man who is much harder, who seems to have embraced and embodied the royal institution'.
The ABC report also said Harry is willing to end the rift between William, had tried to reach out to his brother and that relations with his father Charles 'may be on the mend'.
Mr Scobie said: 'There is a steady open line of communication between the two, where they are able to talk with each other. Where Harry, I would say, clearly understands that his father probably isn't the most emotional or open person'.
The report on ABC said its interview with Mr Scobie also saw him claim he felt he was caught up in a family drama - and that Meghan contacted him to check he was OK.
ABC claimed Mr Scobie also says that he is not that close with Harry and Meghan and he 'never chose Team Sussex'.
William, Harry, Meghan and Charles speak together at Westminster Abbey in March 2019
Meghan, Harry, William and Kate on the balcony of Buckingham Palace in July 2018
The interview will be broadcast tomorrow night on Nightline.
Mr Scobie tweeted a link to the interview on X today, adding: 'More of this @GMA interview will be aired Tuesday on @ABC @Nightline and I'll be live in the studios for @ABCGMA3 and @ABCNewsLive tomorrow, the global release day of #ENDGAME.'
Mr Scobie's book is said to make a series of claims involving the Sussexes - including that William was involved in 'things that have gone out about his own brother', that the elder brother ignored texts from Harry when the family were making their way to Balmoral before the late Queen died last year.
Among the claims made in the book are that there is a rift between the King and the William, that Queen Camilla has 'quietly thanked' Piers Morgan for 'defending the Firm' and that a timid Princess of Wales has to be encouraged to perform engagements.