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."
Mr Hannigan described leading the men and women of GCHQ as a "great privilege".
He wrote: "I am proud of what we have achieved in those years, not least setting up the National Cyber Security Centre and building greater public understanding of our intelligence work.
"I am equally proud of the relentless 24-hour operational effort against terrorism, crime and many other national security threats. While this work must remain secret, you will know how many lives have been saved in this country and overseas by the work of GCHQ.
"Underpinning this is our world-class technology and, above all, our brilliant people.
"As you know, I have also initiated the greatest internal change within GCHQ for 30 years, and I feel that we are now well on the way to being fit for the next generation of security challenges to the UK in the digital age."