Harry Potter author JK Rowling has quit as patron of the MS Society Scotland, claiming the charity is being torn apart by an internal row.
The multi-millionaire, who has supported the charity for nearly a decade, said conflict between the Scottish charity and management in London had resulted in a raft of other resignations.
She said: "I have now reluctantly decided that I cannot, in good conscience, continue to be the public face of a charity that is changing beyond recognition from the one with which I have been so proud to be associated."
The author's mother died from the disease at the age of 45 in 1991.
She said she had taken the decision to stand down "with profound sadness and regret" but added that her financial support of a research project at Edinburgh University would continue.
She said in a statement: "I also remain committed to financing future research into the treatment and causes of Multiple Sclerosis, and to campaigning for better care and treatment of people with MS in Scotland, which is the MS capital of the world.
"This disease claimed my mother's life at the age of 45, and I hope to continue giving both time and money to a cause which remains so close to my heart.
"I have not taken the decision to quit my position as patron of MSSS lightly. Late last year, I initiated and attended a mediation session, in the hope of sorting out long-standing and escalating conflict between the Scottish Council and management in London, driven by the imposition of changes by London.
"Unfortunately, this achieved very little. With mounting frustration and disappointment, I have witnessed resignations of immensely dedicated people within MSSS and the increasing demoralisation of staff whom I have come to know and admire over the ten years of our association."
She said her disappointment "cannot be overstated. Nevertheless, I hope to continue to play a part in combating the underfunding and misunderstandings surrounding MS for many years to come. I shall also continue to hope that the MS Society Scotland manages to resolve its difficulties."
An MS Society spokesman said: "JK Rowling has been a great patron for the MS Society Scotland for many years. We are sorry she is stepping down and thank her for her good work, and for her continued support for the MS research centre in Edinburgh.
"The Society is in the middle of a governance review to make sure we are properly organised to build on the excellent work we already do in Scotland and across the UK. We are a strong, democratic organisation and this review is being done in consultation with all of our 43,000 members.
"We would have preferred to do this with JK Rowling's involvement, but we appreciate that significant change can be difficult. We would urge supporters of the MS Society to work with us now. The Board is confident that what we are doing is all about delivering the best possible support to over 10,000 people living with MS in Scotland."