Liz Truss has resigned as Prime Minister after serving for just over six weeks, following a number of economic U-turns, resignations, and a night of chaos in the House of Commons.
Speaking outside Number 10, she said a leadership contest would be launched - with a new Prime Minister in place within a week.
One name floated as a possible contender was that of her new Chancellor, Jeremy Hunt. But he's ruled himself out, having stood twice to be leader in the past and suggesting that it would be against the wishes of his family.
So here, we look at some of the other key runners and riders who could become our next Prime Minister.
Mr Sunak will "certainly" run again to be leader, according to MP Richard Holden, who represents North West Durham,
The former chancellor and the defeated leadership contender was the favourite among MPs in the recent leadership race.
Truss's fiscal U-turn on one of the biggest tax cuts announced by sacked chancellor Kwasi Kwarteng, effectively meant the current government opted to stick with Sunak's plans.
The tax cuts would have cancelled the plan introduced by Sunak to bring the corporation tax rate to 25% in April next year, from 19% currently.
Truss' backtrack gives Sunak the advantage of being seen as a safe pair of fiscal hands.
But he's not popular with some Tories on the right of the party, seen by some as key in toppling Boris Johnson, and by others as enacting massive spending plans at odds with typical Conservative economics.
There have been reports that some MPs were looking to install Rishi Sunak and Penny Mordaunt – on a joint ticket at the head of a new administration.
At third place in the Conservative leadership race, the former defence secretary is another favourite among Tory MPs - plus a bookies favourite.
Tory MP Crispin Blunt, who publicly called on the Prime Minister to quit, gave a leadership team based around Rishi Sunak, Penny Mordaunt and Jeremy Hunt as his preference.
Penny Mordaunt, now the Leader of the House of Commons, stood in for Truss answering questions from opposition leader Keir Starmer in the Commons on Tuesday.
In the aftermath of Ms Truss's resignation both The Times and The Telegraph reported that Mr Johnson sill stand to be leader.
The former Prime Minister still has allies within the party, with former Culture Secretary Nadine Dorries saying that were Liz Truss to stand down, the next leader should be Mr Johnson or "a general election."
He was the last leader to win a mandate from the public, winning a large majority in the 2019 general election.
But after being forced from office after a number of scandals, he could be a bitter pill for many MPs - and the country - to swallow.
Defence Secretary Ben Wallace has also been flagged as a potential replacement.
He didn't stand in the Conservative leadership race, despite calls for him to do so, but he's a popular minister widely respected for the role he has played in the UK's support for Ukraine.
There had been recent speculation that including the Ministry of Defence in any round of spending cuts could spark a clash with Wallace - who wants the government to commit to an increase in defence spending to 3% by 2030.
The Home Secretary until Wednesday resigned after breaching security protocols.
She's popular on the right wing of the party, favouring a tough line on immigration and once said it was her "dream" and "obsession" to see a plane depart for Rwanda carrying migrants.
She also stood in the leadership contest, and, despite being knocked out in the second round, won the support of key MP Steve Baker, who is influential on the right of the party.
What about Sir Keir Starmer?
As leader of the opposition, Sir Keir would almost certainly have to win a general election to be Prime Minister - which means a general election would need to be held.
With incredibly high support in the polls for the Labour party, it's very unlikely that Conservative MPs would vote to hold an election that could cost many of them their seats.
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