Kate Middleton and Meghan Markle. (Photo/Courtesy)

The Duchess of Cambridge didn't always offer enough support to Meghan Markle as she learnt the ropes of royal life, the author of a new biography has claimed.

Omid Scobie, who penned the highly-anticipated Finding Freedom with Carolyn Durand, says that while there wasn't a fallout between the two women as such, they didn't really click.

Speaking on Good Morning America ahead of the book's release tomorrow, he said: "These are two women who really have little in common.

"Being a newcomer, and knowing Kate was once a newcomer, I think there were times where she knew that Meghan felt that she could have, or needed a bit more support from Kate, but didn't get it in some of those important moments."

Asked about the story of Meghan making Kate cry at a bridesmaid dress fitting, he said "it couldn't be further from the truth".

Extracts of the book published last week support this point, but say there were a few "awkward" moments between the two women.

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The authors write that while there were no rows as such, there were some "awkward moments" between the royal wives.

It is claimed Meghan had hoped Kate would reach out to her, but "didn't lose sleep" over it when she did not.

The book 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."

Speaking more generally about Meghan and Harry's time in the royal family, Scobie said: "History will remember them as a couple who were perhaps failed by the institution of the monarchy.

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"Where there was this chance to have a woman of colour, an American woman of colour, 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, inclusively and representation in a way that no other moment in their lives could have brought.

"For them to not have harnessed that is something I'm sure historians will be looking at in years to come."

A statement from Meghan and Harry's team claim they had nothing to do with the book. The authors claim it has been put together from 100 interviews with those closet to the couple.