Prince Harry was left angry at the start of his relationship with Meghan after his brother William referred to her as "this girl".
New extracts from a book about Harry and Meghan's split from the Royal Family claim to reveal details of a conversation between the brothers.
"Don't feel you need to rush this," William told Harry, according to sources quoted in the book, Finding Freedom. "Take as much time as you need to get to know this girl."
The extracts - quoted in The Sunday Times - explain how Harry heard a "tone of snobbishness" that was "anathema to his approach to the world" in the words "this girl".
The new claims also include the supposed reaction of the wider royals when Meghan first came onto the scene.
"Meghan had often been the topic of conversation and gossip among them. When she arrived in the prince's life, one senior royal referred to the American actress as 'Harry's showgirl'," the book says.
"Another told an aide, 'She comes with a lot of baggage.' And a high-ranking courtier was overheard telling a colleague, 'There's just something about her I don't trust.'"
When describing Meghan's relationship with Kate, the authors say that the pair never really spent much time together before Meghan and Harry's wedding and they never got any closer afterwards - despite Meghan becoming a senior royal.
But the book adds that while there were some "awkward moments", the duo never had a falling out.
It says: "Meghan would agree with the assessment that the duchesses were not the best of friends. Their relationship hadn't progressed much since she was Harry's girlfriend.
"But they were not at war with each other, either. There were awkward moments, such as the day the women happened to cross paths at Kensington Palace (in early 2017, when Harry and Meghan were still only dating), and although both were heading out to go shopping - in the same street - Kate went in her own Range Rover."
The Sussexes, who married in 2018, now live in Los Angeles with their 14-month-old son Archie after stepping down from royal duties in March.
While the media speculated that Meghan was behind the decision for the couple to step back, the book says she was "willing to do whatever it takes" to make it work.
Meghan is said to have told a friend in March: "I gave up my entire life for this family. I was willing to do whatever it takes. But here we are. It's very sad."
A previous extract of the book, published on Saturday morning, alleges that the relationship between the Duke and Duchess of Cambridge and Duke and Duchess of Sussex was extremely bitter by March this year, and they didn't even speak during a service at Westminster Abbey.
"While Harry and Meghan both greeted William and Kate with smiles, the Cambridges showed little response," the book says. "It was the first time the two couples had seen each other since January."
The book claims William nodded at Harry to acknowledge him, but ignored Meghan.
"Although Meghan tried to make eye contact with Kate, the duchess barely acknowledged her," the book adds.
But, according to the authors, the rift stemmed from Harry feeling suffocated by his brother, rather than the "duelling duchesses".
The authors wrote: "The truth was that Meghan and Kate just didn't know each other that well."
But rumours that Meghan made Kate cry during a bridesmaid's dress fitting for Princess Charlotte are false, the book insists.
Those present were "puzzled" at reports Meghan's "strict demands" had left Kate in tears and a source who was there said: "Some of the children weren't co-operating, and there was a lot going on.
"Everyone tried to help where they could, but it's never easy with kids at fittings. There were no tears from anyone.
"And in the end, the fitting was fine. Kate and Meghan were both a little stressed but professional in the room, and there were other people there."
The book also claims Meghan felt sorry for her estranged father, wanted him at her wedding, and blamed the media for "corrupting" him.
Meghan felt let down when Thomas Markle lied to her by denying he helped the paparazzi stage photos of him going about his life in a Mexican resort town before the royal wedding, but she and Harry were also angry with the media for persisting until he gave in.
According to an unnamed "trusted confidant" of the duchess, Meghan had said: "My dad never sought this out. I really believe that he's the victim, and now I feel sad because I believe he's been fully corrupted."
Mr Markle did not attend the wedding in the end, partly due to a heart attack days beforehand which he blamed on the stress.
"As much as she was hurt and humiliated, she wanted him to be there and was willing to move on," an unidentified friend of Meghan's is quoted as saying.
"Plus, she was worried about him; she honestly wasn't sure if he was actually OK. His behaviour was bizarre."
A spokesperson for Meghan and Harry said: "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 statement added.
Finding Freedom is due to be published in August and is being serialised in The Times and The Sunday Times.
Analysis: Brothers' distance 'troubling and upsetting'
By Rhiannon Mills, royal correspondent
"Revenge is sweet, Rhiannon, revenge is sweet," was Prince William's reply when I asked him in 2018 what it was like to be asked to be Prince Harry's best man.
It was the usual banter I'd come to expect from the brothers and at that point there were no real signs of the rift now being laid bare in this book.
Certainly we've heard rumours that they weren't getting on, so it's not exactly a surprise, but this does give us uncomfortable details about what was going on, at least from the Sussexes' perspective.
Words like snobby don't look good for an institution that's worked so hard to be relatable.
But I think there'll be many who'll just see this as incredibly sad.
There's been a huge fondness in this country for the two brothers.
We've seen them grow up and they couldn't have seemed closer, so to think that bond has broken down after everything they've been through is troubling and upsetting.