Just two days ago Liz Truss declared she was a “fighter, not a quitter” in a defiant exchange with the leader of the opposition – a little over 24 hours later she had resigned.
Here, Sky News looks at the runners and riders to replace the prime minister.
Live politics updates as third cabinet member backs Johnson
The leader of the Commons was the first to announce a bid to become the next prime minister.
“I’ve been encouraged by support from colleagues who want a fresh start, a united party and leadership in the national interest,” she said in a post on social media.
“I’m running to be the leader of the Conservative Party and your prime minister – to unite our country, deliver our pledges and win the next GE.”
She finished in third place in this summer’s Tory leadership race before she backed Ms Truss’s bid.
The former defence secretary caused a stir at the Tory conference earlier this month when she said the party’s “comms is s***”.
In messages shared in Conservative Party WhatsApp groups, leaked to Sky News, Tory MP Crispin Blunt called for Mr Sunak and Ms Mordaunt to take over.
“Step forward Rishi and Penny, with our support and encouragement in the interests of us all,” he wrote.
Ms Mordaunt was sent to the Commons on behalf of Ms Truss to answer an urgent question on the sacking of former chancellor Kwasi Kwarteng on Monday. She denied that Ms Truss was hiding “under a desk”.
Former Commons leader Andrea Leadsom is among those who have publicly declared their backing of Ms Mordaunt.
The former chancellor, who was runner-up to Ms Truss in the Tory leadership race, is favourite with the bookmakers to replace her.
He warned his rival her tax-cutting plans would send the economy into freefall, accusing her of “fairytale economics” as she promised unfunded tax cuts.
Following the fallout from the mini-budget, supporters of Mr Sunak believe he has been vindicated. One MP who supported him in the leadership race told The Telegraph: “Everything he said has come to pass.”
Mr Sunak won every voting round among MPs in the Tory leadership race but there are question marks over whether he could reunite the party, having been seen to have played a key role in Boris Johnson’s exit as PM.
Many MPs have come out in support of the former chancellor, the most notable being former deputy PM Dominic Raab and former environment secretary George Eustice.
In his farewell address as PM, Mr Johnson fuelled speculation about a future return to frontline politics despite promising his “most fervent support” to his successor Ms Truss.
Mr Johnson compared himself to Roman statesman Cincinnatus, who battled against invasion before returning to his farm. According to tradition, Cincinnatus later returned to serve a second term.
Some Tory MPs are reportedly openly suggesting the party asks Mr Johnson to return to Downing Street, despite being ousted just three months ago.
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Former culture secretary and ally of the former PM, Nadine Dorries, is one of those openly calling for Mr Johnson’s return.
“Only one MP has a mandate from party members and from the British public – a mandate with an 80 seat majority. Boris Johnson,” she said.
Jacob Rees-Mogg was the first cabinet minister to publicly declare his backing for the former prime minister, posting on social media: “I’m backing Boris #BorisorBust.”
In ruling himself out of the race, Ben Wallace, the defence secretary, said he is “leaning towards Boris Johnson”.
Levelling Up Secretary Simon Clarke has also expressed his support for Mr Johnson’s return.
Sky News also understands former home secretary Priti Patel will back Mr Johnson if he chooses to run.
Although multiple Tory MPs have expressed their support for a Johnson comeback, he remains a divisive figure.
Foreign Office minister Jesse Norman said selecting Mr Johnson as Conservative leader would be “absolutely catastrophic”.
Sir Roger Gale, the senior backbencher, reminded voters in a tweet that the former prime minister, who resigned in a mire of sleaze, remains under investigation by the Commons privileges committee for potentially misleading the House over partygate.
If found guilty, Mr Johnson could face recall proceedings and potentially lose his seat in a by-election if he receives a suspension of 10 days or more.
The Liberal Democrats are calling for Mr Johnson to be blocked from standing as leader of the Conservative Party and prime minister.
Ms Braverman was the first to declare she was running to be the next Conservative Party leader in the summer, praised as a figurehead of the right of the party for her hardline views on Brexit and for denouncing “woke nonsense”.
She threw her hat in the ring for the Tory leadership even before Mr Johnson had officially resigned.
“I love this country. My parents came here with absolutely nothing and it was Britain that gave them hope, security and opportunity and afforded me incredible opportunities in education and my career,” she told ITV at the time.
“I owe a debt of gratitude to this country and to serve as prime minister would be the greatest honour so yes I will try.”
After her shock resignation as home secretary on Wednesday for sharing secure information through a private email, Ms Braverman lashed out at Ms Truss’s “tumultuous” premiership and accused the government of “breaking key pledges” – including on immigration policy.
Ms Braverman, a former attorney general, only became home secretary on 6 September when Ms Truss brought her in to replace Priti Patel.
Her tenure was controversial, having accused Tory critics, who successfully forced Ms Truss into U-turning over plans to scrap the top rate of income tax, of a “coup”.
A source close to rising star Kemi Badenoch has suggested to Sky News that she is set to stand in the leadership contest.
“Now that the prime minister has announced her resignation, the party must unite around a new leader who restores trust in politics and delivers good government for the British people,” the source said.
“Kemi is in conversations with colleagues about how best to achieve this.”
Ms Badenoch stood in the Conservative leadership race over the summer, coming fourth behind Mr Sunak, Ms Mordaunt and Ms Truss.
Little known beyond Tory circles at the start of the race, the former equalities minister was a favourite among members to the right of the party.
Her summer campaign focused on cultural issues which she said had divided the party in recent years.
Sky News understands the current justice secretary is taking soundings on whether to stand in the leadership election.
It is understood he could stand on a possible platform of being a pragmatist and a unifier.
Mr Lewis did not stand in the last leadership election, instead backing outgoing PM Liz Truss.
He has also served as Northern Ireland secretary.