A new book about Prince Harry and Meghan says Prince William feared his brother had been "blindsided by lust" in his haste to wed the US actress.
In Finding Freedom, serialised by the Times and the Sunday Times, the authors claim Harry was angered by what he perceived as his brother's "snobbish" attitude to his bride.
The book's co-authors, Carolyn Durand and Omid Scobie, claim Harry was offended by William's advice to "take as much time as you need to get to know this girl".
According to the pair, William was happy for his brother, but "just wanted to make sure that Harry wasn't blindsided by lust".
But his younger brother allegedly took offence to the phrase "this girl", and interpreted it as "snobbish and condescending".
The rest of the royals were also apparently less than welcoming, with one senior royal allegedly referring to Meghan as "Harry's showgirl" - and another saying "she comes with a lot of baggage".
Another senior courtier is said to have told a colleague: "There's just something about her I don't trust".
Harry's belief that the palace was out to sabotage his relationship was the beginning of the rift with his brother.
He is said to have felt "unprotected" by the institutions around the monarchy, and derided by the old guard for being "too sensitive and outspoken".
Kate, the Duchess of Cambridge, apparently did little to bridge the divide and never really got to know Meghan.
One source said of Harry: "He's extremely protective of Meghan.
"He understands that a lot of people are against them, and he will do everything he can to keep her safe and away from getting hurt - even if that means distancing himself from those people."
Another said the coolness between the princes was the reason for Harry and Meghan's move to Windsor.
"He wanted to get away from the goldfish bowl that was Kensington Palace," the said.
"Everywhere you turn, you're surrounded by staff and family. He was at a point in his life where he was working with his brother, doing the foundation with his brother and living by his brother.
"It was too much."
Other claims include that
* The two couples hardly spoke at the Commonwealth service at Westminster Abbey in March, despite not having seen each other since January.
* The Sussexes felt their complaints were not taken seriously and believed other royal households were leaking stories about them to the press.
* Being told to operate under Buckingham Palace's umbrella after splitting their household from the Cambridges was "a big disappointment" to the Sussexes.
* The Sussexes even considered breaking protocol by springing a surprise visit on the Queen when they believed they were being blocked from seeing the monarch.
A spokesman for Harry and Meghan said the couple did not contribute to the book, but he did not deny the content of The Times's extracts.
The spokesman told the PA news agency: "The Duke and Duchess of Sussex were not interviewed and did not contribute to Finding Freedom.
"This book is based on the authors' own experiences as members of the royal press corps and their own independent reporting."
The revelations come after the Sussexes launched legal action in Los Angeles after drones were allegedly used to take pictures of their 14-month-old son Archie.
A complaint filed at the Los Angeles County Superior Court on Thursday claims an unnamed individual photographed Archie at their home during lockdown.
The lawsuit is the latest example of the couple's war against what they describe as an intrusive tabloid media.
Meghan is suing Associated Newspapers, publisher of the Mail on Sunday and MailOnline, over articles which featured parts of a "private and confidential" letter from the duchess to her estranged father, Thomas Markle.