Boris Johnson's cabinet reshuffle, which triggered the shock resignation of Chancellor Sajid Javid, has provoked debate online over whether the UK PM's chief adviser Dominic Cummings is in fact calling the shots in government.
He is replaced by Sunak, who was until now Javid's junior as the Chief Secretary to the Treasury and seen as a rising star within the Cabinet.
Downing Street says a new joint team of special advisers is being established to advise both the prime minister and the chancellor.
This is now being replaced with an integrated Number 10-Treasury team of advisers at the top of that structure.
Johnson also sacked Northern Ireland Secretary Julian Smith - another surprise move.
Before the explosive meeting with Mr Johnson, Mr Javid had walked smiling into Number 10 in a sign that he expected to remain in place ahead of the March 11 Budget.More news: Senate votes to limit Trump's war powers on Iran, presidential veto expected
Javid's resignation followed reports he had clashed with Johnson's powerful adviser, Dominic Cummings, a self-styled political disruptor who is mistrusted by many lawmakers and officials.
"I think the prime minister has to choose who's in the cabinet, who serves", stated Smith.
Meanwhile Liz Truss, the MP for South West Norfolk who had been tipped for a demotion, kept her job as secretary of state for worldwide trade.
Andrea Leadsom and Esther McVey are among others no longer in government.
But along with the ministerial exits, the reshuffle - which Downing Street insiders had predicted would be "conventional" before the row with Mr Javid - saw promotions for MPs who are highly rated by Number 10.
He used Thursday's reshuffle to announce Alok Sharma as his new business and energy minister, with a new responsibility for running the United Nations climate talks in Glasgow in November.More news: World Health Organization chief claims, 'Corona virus may end in two months '
Anne-Marie Trevelyan joins the cabinet as global development secretary, having previously been a defence minister.
Former Brexit minister Suella Braverman returns to the government as attorney general.
Smith had been widely praised for helping to end political deadlock that left Northern Ireland without a regional government and assembly for three years.
Foreign secretary Dominic Raab, de-facto deputy prime minister Michael Gove, and meanwhile, will keep their current positions.
But allies of the axed minister said it was "absolute crap" to suggest that Mr Johnson and Number 10 had not been kept informed of the process and details of the deal.
Former culture secretary Baroness Nicky Morgan had already said she was leaving her role, while Leadsom, Villiers and McVey were all sacked.More news: Netflix defends itself against new transmission rivals through the Samsung association