Palmerston, the Foreign Office's resident cat, has retired from mousing duties to "spend more time relaxing away from the limelight".
In a "letter", he says he has moved away from Whitehall and is now climbing trees rather than "overhearing all the foreign dignitaries' conversations".
The black-and-white rescue cat, who has more than 105,000 Twitter followers, arrived from Battersea in 2016.
He has been known to clash with Larry, Number 10's main mouse-catcher.
Their decidedly undiplomatic disputes - which have included several hissy fits and a stand-off in full view of the press in Downing Street - are not thought to have hastened his departure.
Named after the famously interventionist and amorous 19th-Century Foreign Secretary and Prime Minister Viscount Palmerston, Palmerston has often featured in photographs involving visiting officials.
In a distinctly anthropomorphic letter sent to Foreign Office permanent secretary Sir Simon McDonald, Palmerston "writes" that while there, he "pawed numerous memorandums" and set up his own "parallel network" for intelligence gathering.
He adds that, during the pandemic he, like so many other civil servants, has decided to "work from home" rather than in the office, while remaining "as diligent as ever".
Palmerston, whose age in cat years is uncertain, making a pension doubtful, has moved to an undisclosed location "in the countryside".
He promises to remain "an ambassador for the UK" and praises his fellow "diplocats" and "diplodogs".
Palmerston, whose letter mercifully refrains from puns on "paw-licy" and contractual "claw-ses", says he will enjoy more "me time" over the summer and beyond.
A replacement has yet to be appointed, to the probable delight of Foreign Office mice, who have yet to comment.
Possible names for Palmerston's successor - assuming the link to former foreign secretaries is maintained - include Canning, Bathurst, Balfour, Eden, Rifkind and Miliband.