The document said Jason Knauf was required by "palace protocol" to inform more senior aides in the royal households that Meghan was going to write to her father.
Meghan, Britain's Duchess of Sussex, sought advice from two senior members of the royal family before writing a letter to her father which is at the centre of a privacy lawsuit against a tabloid newspaper, court documents show.
The document did not name the members of the royal family who advised Meghan.
Thomas Markle told Good Morning Britain that doing media appearances was his "only shot" at speaking to the pair.
Her reason being that she was concerned that her father, Thomas Markle's claims about her cutting him out of her life, would be repeated.
Meghan Markle has been estranged from her father Thomas Markle since tying the knot to Prince Harry in a lavish ceremony in 2018
Meghan's legal team insisted the letter was not a media strategy but an attempt to protect the duchess and her family including the royals "from further media intrusion and embarrassment to the institution".
Thomas Markle hinted he may have some royal grandchildren to enjoy soon. Their son, Archie, was born the following year. Associated Newspapers' lawyers argue that Meghan made personal information public by cooperating with the authors of the book to set out a version of events favorable to her.
Thomas Markle also revealed he hasn't met his grandson, 1 NEWS Europe correspondent Daniel Faitaua reports. But Meghan did allow an unidentified individual to communicate the "true position" on one aspect of her relationship with her father to the authors, the new document says.
At a High Court hearing last month, Mr Justice Warby, who is overseeing the case, agreed to Meghan's application to adjourn the trial - which was due to start on January 11 next year - until next autumn after hearing from lawyers for both parties in a private hearing. However, in a ruling earlier yesterday, the judge Mark Warby said Markle did not appear to be an important witness in the case and it was inaccurate to view it as a family battle.
The rift between Prince Harry, Meghan and Queen Elizabeth is widening, according to a royal expert.