The head of GCHQ has announced he is to step down as head of the intelligence agency.
Robert Hannigan informed Foreign Secretary Boris Johnson of his intention to leave the post for personal reasons.
He was appointed director of the organisation - often referred to as Britain's listening post - in 2014.
In a letter to Mr Johnson, Mr Hannigan wrote: "After a good deal of thought I have decided that this is the right time to move on and to allow someone else to lead GCHQ through its next phase.
"I am, like you, a great enthusiast for our history and I think it is right that a new Director should be firmly embedded by our centenary in 2019. I am very committed to GCHQ’s future and will of course be happy to stay in post until you have been able to appoint a successor.
"I have been lucky enough to have some extraordinary roles in public service over the last twenty years, from Northern Ireland to No.10, the Cabinet Office and the Foreign Office. But they have all demanded a great deal of my ever patient and understanding family, and now is the right time for a change in direction.
"I want to thank you and the many Ministers I have served over the years, and to thank the Prime Minister and her three predecessors, for the opportunities I have been given.
"I have worked with outstanding people, whether politicians or Crown Servants, and none more so than in GCHQ. I am very confident that they will continue to achieve even greater things in the future."
In response, Mr Johnson said: "You have led the renewal of some of our most important national security capabilities, which we continue to depend on every day to save lives from terrorism and to protect our interests and values.
"You also set the groundwork for a major transformation of our cyber defences, and put GCHQ on a path to meet the challenges of the future with your focus on technology and skills.
"Following your successful tenure, and thanks to the work of thousands of excellent GCHQ staff, the organisation is well placed to play its part continuing to protect our nation.
"I wish you the very best for your future career."