The 47-year-old was hired by series creator Peter Morgan to help write the script for the forthcoming series of the show.
The latest season is set to focus on the conflict between Charles and Diana in the early 1990s until her death in a car crash in Paris on August 31, 1997.
When Morgan, 57, approached her for the role, she was keen to do it because “it was really important to me that the final years of my friend’s life be portrayed accurately and with compassion, as has not always happened in the past”.
But she later backed out of the project because its depiction of Diana was not handled as “respectfully or compassionately” as she had hoped.
Ms Khan told the Sunday Times: “In 2019, Peter Morgan asked me to co-write on the fifth series of The Crown, particularly those episodes which concerned Princess Diana’s last years before she died. After a great deal of thought, having never spoken publicly about any of this before, I decided to contribute.”
She added: “We worked together on the outline and scripts from September 2020 until February 2021.
“When our co-writing agreement was not honoured, and when I realised that particular storyline would not necessarily be told as respectfully or compassionately as I had hoped, I requested that all my contributions be removed from the series and I declined a credit.”
Before she quit the role, Ms Khan had worked on storylines on Diana’s relationships with heart surgeon Hasnat Khan and Egyptian film producer Dodi Fayed, as well as her bombshell BBC Panorama interview with Martin Bashir.
Ms Khan had a brief romance with screenwriter Morgan earlier this year – but he has now rekindled his relationship with actress Gillian Anderson, who played Margaret Thatcher on the show.
A spokesman for The Crown said: “Jemima Khan has been a friend, fan and a vocal public supporter of The Crown since season one.
“She has been part of a wide network of well-informed and varied sources who have provided extensive background information to our writers and research team — providing context for the drama that is The Crown. She has never been contracted as a writer on the series.”
Ms Khan is a former a journalist and associate editor of current affairs weekly the New Statesman. She was formerly married to Pakistani Prime Minister Imran Khan and the pair have two sons.