The charity Arthritis Care has announced that Neil Betteridge, its chief executive, has left the charity.
Betteridge worked for Arthritis Care for 11 years, the past six-and-a-half as chief executive. His last day in the job was Friday.
Rosemary Blair, chair of the charity, said in a statement the organisation was "very sad to see him go".
She said he was "moving on to pursue new career options". A spokesman for the organisation said he did not know if Betteridge had another job to go to.
"The board joins with me in expressing our warmest thanks to Neil and in wishing him every success in the future," said Blair.
"Under his leadership, Arthritis Care has become a leading and respected voice of people with arthritis. He leaves a legacy of policy change and service delivery that we will continue to build on."
Blair said the charity would start the search for a new chief executive shortly.
Betteridge said that, having grown up with arthritis as a child, being chief executive of the charity had "been a dream come true".
"I believe that now is the right time for me to be seeking new opportunities at a personal level," he said in a statement. "It also means Arthritis Care can appoint a successor who will have time to develop and deliver the next long-term strategy, as we approach the final year of the current plan."