The relationship between Princes William and Harry, who were once close, supposedly began to sour when Harry started dating his now-wife Meghan, according to "Finding Freedom." The new book claims to shed light on what caused Harry and Meghan to step back as working members of the royal family.

William, who at that point had only met Meghan, an American actress, a handful of times, reportedly told Harry, "Don't feel you need to rush this . . . take as much time as you need to get to know this girl," while the pair were dating, according to the book.

William's reported comment is said by the book's authors, Omid Scobie and Carolyn Durand, to have had a chilling effect between the brothers, the only children of Prince Charles and the late Princess Diana.

While much of the attention around Harry and Meghan's split from the royal family has focused on the reportedly tense relationship between Meghan and Prince William's wife, Duchess Kate, the focus should be more on growing pains between William and Harry, according to Scobie.

"I felt it important to really dive into this in the book because we had seen Meghan and Kate really blamed for almost driving a wedge between [Princes William and Harry]," Scobie, an ABC News royal contributor, told " Good Morning America." "They're both men in their 30s, and [it was] Harry not wanting to play that role of sort of the younger, more subservient brother anymore."

Scobie said it is true that Meghan, a California-born former actress, and Kate, a U.K. native who met William while studying at St. Andrews in Scotland, have "very little in common." Sources told him that Meghan felt she didn't get all the support she needed from Kate as a newcomer to the royal family.

He shot down, though, a widely-reported story that Kate was left in tears over a conflict with Meghan in the days leading up to her high-profile 2018 wedding to Harry.

"When I spoke to the people who were actually there and involved, the first thing they all said, 'Well, there were no tears,'" said Scobie. "[The story] couldn't be further from the truth."

The relations between the two couples, the Sussexes and the Cambridges, were however so strained the Cambridges snubbed the Sussexes at their final engagement as working members of the royal family, according to "Finding Freedom."

"While Harry and Meghan both greeted William and Kate with smiles, the Cambridges showed little response," Durand and Scobie wrote about this year's Commonwealth Day service in March at Westminster Abbey.

Friends of William and Kate are striking back at claims that Kate did not welcome Meghan into the family. Sources close to the couple told the Daily Mail on Sunday that the Cambridges had "rolled out the red carpet" for Meghan.

"It's really sad because they grew up together, side-by-side supporting each other through the most difficult of times," ABC News royal contributor Victoria Murphy said of the divide between William and Harry, who supported each other through the death of their mom more than 20 years ago.

Scobie noted that Meghan did face apparent struggles to settle into the monarchy upon her marriage to Harry. She entered into Britain's royal family not only as an American but also a biracial woman who was also a divorcee.

"In terms of ticking those boxes that may ruffle feathers within an ancient institution such as the monarchy, she ticked them all," he said. "Race absolutely played a role."

Scobie predicted that history will remember Harry and Meghan as a "couple that were perhaps failed by the institution of the monarchy.

"Where there was this chance to have a woman of color, an American woman of color in the House of Windsor, representing the monarchy just as much as her husband, that was a chance for the royal family to have diversity, inclusivity and representation in a way that no other moment in their lives could've brought," he said. "And for them to not have harnessed that is something that I'm sure historians will be looking at for years to come."

Buckingham Palace is not commenting on "Finding Freedom," which goes on sale on Tuesday, Aug. 11th.

The Sussexes appear to be trying to distance themselves from the book, of which there has been speculation about how closely they were involved.

A spokesperson for the couple told ABC News in a statement, “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.”

Scobie also told "GMA" that Harry and Meghan were not involved in the book.

"I know there's a lot of speculation about the couple having sort of given secret interviews for the book and having weighed in," he said. "But it really couldn't be further from the truth."