The royal aide caught up in both Meghan Markle's court battle with the Mail On Sunday and bullying claims against her is to step down as CEO of Prince William and Kate's Royal Foundation.
Jason Knauf is standing down in December after seven years of working with the Duke and Duchess of Cambridge, as well as time working with Prince Harry and Meghan.
The Times earlier this year claimed he had previously raised concerns that Meghan, while still a senior royal, "was able to bully two PAs out of the household".
Nothing was taken forward at the time he raised the concerns, but the allegations came out shortly before Harry and Meghan's interview with Oprah Winfrey aired in the US.
Buckingham Palace said it would investigate. Meghan said she was saddened by the attack on her character.
The announcement of Knauf's resignation came soon after his name was mentioned in a court ruling involving Meghan, as she battles copyright and privacy infringement with the Mail On Sunday and the MailOnline.
Knauf was named by Associated Newspapers Ltd, the publisher of both titles, as having helped Meghan write a letter to her father that they published extracts of in February 2019.
She has won her case for privacy infringement but ANL was also seeking to argue that because Knauf had helped her with the letter, she was not the sole author and copyright holder.
However, Knauf said he did not seek any right to the authorship of the letter, saying he had made one small suggestion in the course of the discussions about her writing to her father.
In a joint statement announcing his news, the Duke and Duchess of Cambridge said: "Jason has been an integral part of our team since 2015. We are immensely grateful for his hard work and commitment, both at The Royal Foundation and previously as our Communications Secretary.
"Since taking over as Chief Executive, Jason has driven positive change, making our vision for our charitable work and the causes that matter most to us a reality. We are sad to see him go but wish him all the very best in his future career.
"We look forward to launching the recruitment search shortly and welcoming a new Chief Executive later on this year.”
Watch: Royal officials investigating Duchess of Sussex bullying allegations
Knauf said: "Working with The Duke and Duchess of Cambridge has been the privilege of my career. I will always be grateful for the opportunity I have had to support their leadership in the UK and internationally.
"The months ahead will be the busiest time in the Foundation’s history with the first awards for The Earthshot Prize and more progress on our early childhood work. We have a lot to do with our amazing team and all of our partners."
Knauf, who started working for Kensington Palace in February 2015, is moving out of the UK, the palace said, which has necessitated his resignation.
He was credited with overseeing the development and the launch of Prince William's Earthshot Prize, which has been seen as his most ambitious project. Knauf was also praised for developing Kate's work on Early Years.
The foundation also said he steered the response to the COVID-19 pandemic, setting up a fund that donated £1.8m to to causes supporting frontline workers and the mental health needs of the nation.
Lord Hague, chair of the Royal Foundation, said: "The Royal Foundation has benefited significantly from Jason’s leadership over the past two years.
"Working with The Duke and Duchess and the rest of the Foundation team, he has delivered impact on the issues that Their Royal Highnesses care most about while steering the organisation through the COVID-19 pandemic and ensuring that support reaches those who have been most affected.
“I have thoroughly enjoyed working with Jason and wish him well in the future.
"As the search for a new Chief Executive begins, I am looking forward to continuing to build on the inspiring work that has been done over recent years.”
The duke and duchess will begin looking for a new chief executive for the foundation, which manages their charitable and philanthropic work, in the coming weeks, and make an announcement when they have appointed a replacement.
Watch: Meghan ‘saddened’ by ‘latest attack on her character’ amid bullying claim