As the new PM walks into Number 10 he will be greeted with applause by Downing Street staff - but there is one employee who is notoriously hard to impress.
Larry the cat currently holds the official role of chief mouser to the Cabinet Office, a position that's said to date back hundreds of years.
So how have previous PMs warmed to their four-legged civil servant over the years? A cross-species special relationship or a classic case of feline indifference?
In a 2016 interview with the Sunday Times, Theresa May said she was "very happy to see Larry", but hinted she was more of a dog person after growing up with them at home.
She did note there were parts of Number 10 where Larry "rules the roost" with certain seats he expects to sit on. However, her own office chair was not one of them.
Their relationship is unlikely to have improved after Larry was tactically extracted by police before Mrs May's resignation speech amid fears he would upstage the departing PM.
With many outgoing prime ministers in their final days often rewarding or knighting members of their loyal staff, perhaps a chance to repair the relationship still remains.
But the chief mouser is likely to be more interested in the ongoing turf war between him and his Foreign Office rival, Palmerston.
Multiple fights have broken out in front of cameras on Downing Street, with security guards having to step in to rescue Palmerston in October 2016.
In his final Prime Minister's Questions before resigning, David Cameron quashed rumours he and the Downing Street cat did not get on by brandishing a picture of Larry curled up on his lap.
"Sadly, I cannot take Larry with me - he belongs to the house and the staff love him very much, as do I."
In significant moment in Anglo-American relations, Larry even allowed Barack Obama to stroke him during the presidential visit in 2011 with Mr Cameron later revealing Larry was "all right" with him.
Mr Cameron was actually responsible for bringing Larry to Downing Street in 2011. The then four-year-old arrived from Battersea Dogs and Cats Home - his mouse-catching skills honed from his time as a stray.
Before Larry took up occupation, black tabby Sybil - named after the Fawlty Towers character - briefly stalked the streets of Downing Street.
But her home was not No 10, but No 11 with Chancellor Alistair Darling.
The lack of a feline presence in Gordon Brown's HQ raised questions, and Mr Brown's official spokesperson was forced to deny the PM and his wife had a problem with Sybil.
The incoming prime minister had to share his home with the veteran Humphrey, who had already been patrolling the corridors for eight years when the Blairs moved in.
But rumours circled the Westminster village when Humphrey suddenly left.
Downing Street was forced to deny he had been put down, insisting he had instead been re-housed for health reasons.
This led to Conservative MP Alan Clark using a parliamentary question to ask Mr Blair to outline what "steps were taken by Cabinet Office staff to establish the state of health of Humphrey the cat, prior to his departure from Downing Street".
In his response, the prime minister explained that he was sent away due to worries about the "general deterioration in his condition". Reports from the countryside suggested he had "responded very well and put on weight".
In a career spanning 13 years, Wilberforce served under four prime ministers from Edward Heath through to Margaret Thatcher.
According to information revealed by the Home Office in 2005, the earliest record of a chief mouser is from 1929 when a penny a day from the petty cash was requested to feed a cat called Peter.
Peter was succeeded by two more Peters and a Peta, who caused a rift in No 10 because of her lack of toilet training.