Mr Knauf “provided feedback” in the form of “general ideas,” the documents reveal.
The Duchess is suing the Mail on Sunday over the publication of a letter she wrote to her father, claiming it breached her privacy, copyright and data protection rights.
But lawyers on behalf of the newspaper allege that she breached her own privacy because she “permitted” details about her life to be shared with the authors of Finding Freedom, including “information about the letter”.
In September, a month after the biography was published, the newspaper successfully applied to amend its defence in light of its publication.
A ten-day trial scheduled for January was postponed for at least nine months after the Duchess won a delay on confidential grounds.