Bristol-raised Sajid Javid has resigned as chancellor after he claimed the Prime Minister had attached unreasonable conditions to his reappointment in the Cabinet reshuffle.
His shock resignation came after No. 10 demanded he sack his team of aides, something Mr Javid said "no self-respecting minister" could agree to.
Mr Javid said he felt unable to satisfy the PM's demands to remove all of his political advisers, a request that is understood to come from Mr Cummings, who had become irritated by a number of negative briefings to the media that had been attributed to Treasury sources.
In his resignation letter to the Prime Minister, Mr Javid wrote: "While I am grateful for your continued trust and offer to continue in this role, I regret that I could not accept the conditions attached to the reappointment.
"It is crucial for the effectiveness of government that you have people around you who can give you clear and candid advice as I have always sought to do.
"I also believe that it is important as leaders to have trusted teams that reflect the character and integrity that you would wish to be associated with."
He also told the BBC: "The conditions that were attached was a requirement that I replace all of my political advisers.
"These are people that have worked incredibly hard on behalf of, not just the government, but the whole country, [and] have done a fantastic job.
"I was unable to accept those conditions. I don't believe any self-respecting minister would accept such conditions and so therefore I felt the best thing to do was to go."
However, he said that Rishi Sunak, the 39-year-old Treasury minster who will replace him, had his "full support".
The new chancellor will now have no advisers of his own. Instead an "economic unit" of advisers will be shared between No. 10 and No.11.
"The PM has announced the formation of a new Downing Street economic team, it will be based in No.10 and No.11 and will jointly advise the Prime Minister and the Chancellor of the Exchequer as they work to level up the economy across the UK," the Prime Minister's spokesman said on Thursday afternoon.
The strained relationship between Mr Javid and Mr Cummings dates back to last year, when the Vote Leave spinner sacked one of the chancellor's advisers - without his knowledge - for allegedly staying in contact with aides close to his predecessor, Philip Hammond.
The news of Mr Javid's sacking turns what was seen as a modest reshuffle into a more dramatic overhaul.
Mr Javid was born in Rochdale but spent his formative years growing up with his four brothers in a two-bedroom flat above his parent’s shop in Stapleton Road.
The former Downend School pupil was the first person from an ethnic minority background to take over at 11 Downing Street when he was given the role by Mr Johnson in July last year.
His father Abdul arrived from Pakistan in 1961 with the equivalent of only £1 in his pocket.
Mr Javid will remain as MP for Bromsgrove and now move to a seat on the backbench.
Other ministers to have lost their jobs include Kingswood MP and universities and science minister Chris Skidmore, Northern Ireland secretary Julian Smith, business secretary Andrea Leadsom and housing minister Esther McVey.
Attorney General Geoffrey Cox has also been shown the door, and will be replaced by Suella Braverman, as has Theresa Villiers, who was the environment secretary. George Eustice has been promoted from agriculture minister to take her job.
However, amid the chaos, some MPs have been able to breathe a sigh of relief.
North East Somerset MP Jacob Rees-Mogg has emerged unscathed from Boris Johnson's Cabinet reshuffle despite being widely tipped to be sacked.
The Leader of the House was seen taking Business questions on Thursday morning and it was later confirmed that he would stay in post.
He had been rumoured to be in line for a demotion following comments he made about the Grenfell Tower fire, in which he appeared to suggest that the victims perished because they lacked "common sense".
Mr Rees-Mogg later apologised for the comments, which were widely condemned on social media as insensitive and misjudged.
Michael Gove will also stay on as Chancellor of the Duchy of Lancaster, while Dominic Raab remains foreign secretary and Priti Patel stays on as home secretary.
