Meghan Markle was “unwise” to begin a court battle and scored a "completely ridiculous own goal" with unofficial biography Finding Freedom, a royal expert has claimed.

This week, a judge ruled the Mail on Sunday could rely on the book in a High Court privacy case with Meghan and Prince Harry.

The Duchess of Sussex is suing the newspaper’s publisher Associated Newspapers (ANL) over the publication of a letter she sent to her estranged dad, Thomas Markle.

ANL claims Meghan “lost her rights to privacy in the contents of the letter” because “she and her husband cooperated with the authors” of Finding Freedom to put out “their version of events”.

Meghan and Prince Harry’s representatives have repeatedly denied that they collaborated with the authors.

Meghan claims it violated her privacy by publishing a letter she sent to her estranged dad, Thomas Markle

However, royal expert Richard Fitzwilliams believes it could not have been written without their “tacit agreement”.

He told Daily Star Online: “I always thought that it was very unwise of Meghan to have brought this case because royals should stay out of court.”

He continued: “There were so many intimate details in this book, it was only possible that they could have got that information from Harry and Meghan’s friends.

“When the book was published there were no complaints about privacy, that was extraordinary.”

This week, a judge ruled the Mail on Sunday could rely on Finding Freedom

Meghan’s lawyers themselves have called Finding Freedom “extremely anodyne, the product of creative licence and/or inaccurate”.

Justin Rushbrooke QC, representing the Duchess of Sussex, said the “improbability” of Meghan collaborating with the authors was made evident by “comparing what the defendant's own articles said with what the book said about the letter” to her dad.

Mr Fitzwilliams added: “The whole thing is a completely ridiculous own goal…something that is so easily avoidable.

"Even if they had nothing to do with it, in my view their intimate friends would certainly not have spoken to the authors without their tacit agreement.

“They didn’t complain when it appeared and they’re so keen on their privacy and this was full of very intimate details.

Prince Harry and Meghan have repeatedly denied that they collaborated with the book's authors

“It may well count against them when the case comes to court, if it indeed actually does.”

Omid Scobie, who wrote the book alongside Carolyn Durand, said in a witness statement: “[Meghan and Harry] did not authorise the book and have never been interviewed for it.

"The book was always prepared on the understanding that it was to be independent and unauthorised.”

Judge Francesca Kaye said his statement "does not amount to a knockout blow", adding: "It's not what he says but what he does not say which may be instructive at trial."

A 10-day trial is expected to provisionally begin on January 11.

Daily Star Online has approached a representative for Meghan and Harry for comment.