After months of scandal and years of dominating British politics, Boris Johnson has said he will step down as prime minister and the race to replace him is well underway.
The prime minister announced he would be handing over the keys to Downing Street after more than 50 Tory MPs walked out of government in protest at his leadership last week.
Many thought the partygate scandal would cause his downfall, but it appears to have only started it, with the final nail in the coffin being hammered in by the Chris Pincher controversy.
Mr Johnson will remain in place for several months while the race to become Conservative Party leader takes place.
Here's how the Conservative Party will elect a new leader to be PM
On Monday, the timetable and rules of the leadership race, such as how many nominations a candidate will need to progress on to the next round, will likely be announced by the 1922 Committee of backbench MPs, following their meeting.
The two-stage process will then see Conservative MPs whittle down the candidates to two, through voting rounds, before Tory party members decide the winner.
The schedule is likely to be similar to the process which played out before Mr Johnson took over from Theresa May, but in a bid to speed up the process and whittle down the vast field sooner, candidates are likely going to need a higher number of backers to progress on to the next round.
Any Tory MP who wishes to lead the party can nominate themselves to be a candidate in the contest.
They must receive a certain number of nominations from Tory MPs in order to get themselves on the ballot paper.
The number of required nominations is determined by the 1922 Committee and Conservative Party Board. It was eight at the last contest and is likely to be about 20 this time round in a bid to whittle down an already crowded field.
Any MP who does not get the required number of nominations is removed from the contest.
There are currently 11 Tory MPs who have thrown their hat in the ring but it is not clear if they all have enough support to make it onto the ballot.
Big hitters like Rishi Sunak and Liz Truss are expected to easily make it through, but the MPs who have had little Cabinet experience may struggle.
MPs then vote in a series of rounds to reduce the number of candidates.
In the first two rounds, the candidates who don’t meet a certain threshold of votes are eliminated, with the required number again decided by the 1922 Committee.
For all following ballots, the candidate who comes last is eliminated, until there are only two candidates remaining.
In the 2019 leadership contest, the first stage took two weeks and this time around it is expected to be finished in time for parliament's summer recess which starts on July 21.
Deciding a leader
When just two MPs remain on the ballot, the decision is passed to party members around the country.
People who pay for the Conservative Party membership will receive a ballot paper in the post and will be given a timeframe to make up their minds.
The candidates will take part in a series of hustings - a meeting at which candidates in an election address potential voters - and debates in which they will set out their vision for the party and country.
Party members can place their vote at the start of the process if they wish, however they may choose to watch the debates before making up their mind.
Last time the campaigning stage lasted a month but in 2016, before Theresa May was elected, the process was scheduled to last two months but Andrea Leadsom dropped out before it concluded.
Once the process concludes and the votes are counted, the MP with a simple majority will be named party leader, and as a result, prime minister.
At that point, Mr Johnson will go to Buckingham Palace to tender his resignation to the Queen, and the new Tory leader will be invited to take up the role of PM with immediate effect.
How much longer will Boris Johnson remain prime minister?
Mr Johnson has said he intends to remain as prime minister until a successor is in place, expected to be by the time of the Conservative Party conference in October or even, according to ITV News Political Editor Robert Peston, November.
The PM has now managed to replace most of the MPs who left his government.
He has told them that the government will make no major new decisions during the transition period.
In his resignation speech last week, Mr Johnson did not commit to any specifics as to the timetable of his departure.
UK Editor Paul Brand said there were "quite frantic discussions going on among members of the 1922 Committee", the group that sets the rules for the party and determines the timeline of any leadership contest.
One executive on that committee told Paul Brand that it was "not acceptable for him to remain in post until September, October".
UK Editor Paul Brand explains why MPs are increasingly angry at the prime minister's proposed timetable for his departure
Should Mr Johnson decide he cannot remain as PM, he could choose to step down immediately.
In that case, it would be up to him to nominate a stand-in replacement to the Queen until the Conservative Party had chosen a new leader.
That person would be another Tory MP and most likely someone in the Cabinet who had remained loyal. Deputy prime minister Dominic Raab would likely be among those considered.
Could Boris Johnson stand in a leadership election?
It is unlikely. Under the rules, a leader who resigns is not normally eligible to contest any subsequent leadership election.