The Mail on Sunday then published the letter. Meghan is now suing its publisher, Associated Newspapers, for a privacy breach.
The publisher denies the claims, saying Meghan's father wanted the letter published to counteract false impressions her friends had given about it in their interviews.
Meghan said she hadn't given her friends permission to speak, and hit back at the prospect of them being named if they're called to give evidence in the trial.
Her witness statement submitted with her application read: "These five women are not on trial, and nor am I. The publisher of the Mail on Sunday is the one on trial.
The original article featuring interviews with her five friends. Photo / People Magazine
"It is this publisher that acted unlawfully and is attempting to evade accountability; to create a circus and distract from the point of this case – that the Mail on Sunday unlawfully published my private letter.
"Each of these women is a private citizen, young mother, and each has a basic right to privacy.
"Both the Mail on Sunday and the court system have their names on a confidential schedule, but for the Mail on Sunday to expose them in the public domain for no reason other than clickbait and commercial gain is vicious and poses a threat to their emotional and mental wellbeing."
A Mail on Sunday spokesperson said the newspaper had "absolutely no intention" of publishing the friends' identities.
"But their evidence is at the heart of the case and we see no reason why their identities should be kept secret.
"That is why we told the Duchess' lawyers last week that the question of their confidentiality should be properly considered by the court."
Last week, it was revealed that Meghan claimed in court documents that her friends had been "rightly concerned for her welfare" when she was pregnant.
She named them as A, B, C, D, and E in the papers, and they could now be called to testify in the trial.
People magazine described them as "Meghan's inner circle – a longtime friend, a former co-star, a friend from LA, a one-time colleague and a close confidante".
Meghan identified one of them, A, as the person who told People her letter read: "Dad, I'm so heartbroken. I love you. I have one father".
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