Sir Keir Starmer has lost a key aide just two weeks after he was seconded into No10.
Tom Kibasi, a former think tank boss, was recruited to work for Sir Keir as he continues with his Downing Street reset.
After Sir Keir was forced to conduct a major reshuffle following Angela Rayner's bombshell resignation, Mr Kibasi quietly left No10.
The 43-year-old was only brought into Downing Street by Sir Keir's right-hand man, Morgan McSweeney, last month.
He was supposedly undertaking an unnamed strategy project, having already been hailed as the "architect" behind the Prime Minister's successful leadership campaign in 2020.
However, Mr Kibasi is not the first of Sir Keir's aides to have left No10.
The Prime Minister's first Chief of Staff, Sue Gray, was forced out after losing a power struggle with Mr McSweeney last October.
Nin Pandit and Matthew Doyle have also joined Ms Gray out the door.
Ms Pandit's departure sparked serious concerns about whether No10 has a problem with women.
Sir Keir Starmer marking VJ Day earlier this year
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A source close to No10 told The Telegraph that it was a "bad look" for Downing Street to "mishandle" Ms Pandit's exit, adding that briefings against her were "inaccurate and needlessly cruel".
Despite Boris Johnson's ex-Chief of Staff Dominic Cummings labelling Ms Pandit work in the pandemic as "brilliant", the former NHS digital executive was earlier this year accused of being "useless" by No10 insiders.
Rosie Duffield, a former Labour MP who quit the party last year in a fiery row with the Prime Minister over women's rights, suggested Ms Pandit's departure was another example of Sir Keir running a "boys' club".
She said: "This latest staff loss seems to be following the pattern of senior women who appear to be briefed about when out of favour and are moved aside shortly afterwards.
Tom Kibasi was only appointed to his role in No10 a fortnight ago
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"Whether ministers, backbenchers, or No10 staff, it bears out the feeling of many women in the Labour Party that Sir Keir and his closest allies do indeed have a problem with women."
Following Ms Pandit's departure from No10, Tory leader Kemi Badenoch said: “Keir Starmer keeps sacking advisers, losing ministers, and briefing against his own team in the papers.
“Another reset won’t hide the truth – he has no plan, no direction, and needs his red folder to remind him what he stands for.”
However, a spokesman has insisted that the Prime Minister did not lose confidence in Ms Pandit and instead moved her to the new position because of her years of extensive policy-making.
Sir Keir Starmer while addressing the Scottish Labour Conference
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The revolving door for the Prime Minister's advisers also saw Baroness Shafik enter No10 as his chief economic tsar.
Baroness Shafik's appointment raised alarm bells of further tax raids in the upcoming Budget on November 29, given her previous comments about wealth levies.
However, the changes come as the dust settles on the Prime Minister's reshuffle.
Sir Keir conducted his reshuffle shortly after Angela Rayner tendered her resignation over her £40,000 stamp duty scandal.
Angela Rayner's resignation sparks a huge reshuffle
| PASir Keir shifted ex-Justice Secretary Shabana Mahmood to the Home Office, appointed Yvette Cooper as Foreign Secretary and demoted David Lammy to sit in the Ministry of Justice while abating his ally with the role of Deputy Prime Minister.
Lucy Powell was among those culled as the Prime Minister rang the changes.
A number of loyalist new intake MPs also found themselves on the ministerial payroll.
Dover & Deal MP Mike Tapp secured his place in the Home Office, while Mr McSweeney's wife Imoge Walker became Assistant Whip.