It's not often a House of Commons select committee meeting is one of the biggest political events of the year.
But it's also not often the person giving evidence is Dominic Cummings.
At 9.30am on Wednesday, Boris Johnson's controversial former aide is to give evidence about the government's response to the coronavirus pandemic.
Cummings has hinted there will be explosive revelations. So, will Johnson be watching through his fingers? Or will it not actually be that bad for the prime minister?
Here, Yahoo News UK explains everything you need to know ahead of Cummings's committee appearance.
Why is Cummings relevant?
Cummings was Johnson’s chief adviser between July 2019 and November last year, when he famously marched out of Number 10 holding a big box.
Backed by Johnson, the controversial aide had exerted huge control over the government’s agenda and was considered more powerful than most elected ministers.
Watch: Dominic Cummings leaves Downing Street in November
However, the pair reportedly fell out amid a Downing Street power struggle, prompting Cummings’s exit.
At first, there appeared to be a truce, but the fallout has become increasingly bitter in the past two months.
As a result, there is huge interest in what Cummings will say during his appearance before a joint meeting of the Commons health and social care and science and technology committees on Wednesday.
What will the committees ask Cummings?
A press release issued last week read: "The prime minister’s former chief adviser Dominic Cummings will face questions on decisions taken, during his time working in government, to deal with the threat of COVID-19.
"MPs are expected to focus on decision-making in the early months of the pandemic; the level of scientific evidence available to the government; its border policy; and the effectiveness of its public health messaging and communications.
"The timing of lockdowns and other restrictions, procurement processes, and decisions about community testing and contact tracing are among other issues expected to be addressed."
It has been reported the hearing could last four hours.
Is this Cummings's first appearance since leaving Downing Street?
No. Cummings was quizzed by MPs at the science and technology committee on 17 March.
The purpose of that meeting was for him to give evidence on the Advanced Research and Invention Agency (Aria) that he was seen as being the architect of.
However, Cummings also used it to fire his first shots at the government over its handling of the pandemic.
He said responsibility for the coronavirus vaccine programme was removed from Matt Hancock’s “smoking ruin” Department of Health due to the “absolute total disaster” of its initial response to the pandemic.
He added MPs need to take a “very, very hard look” at what the government got wrong during its handling of the COVID outbreak.
The following day, it was announced Cummings had agreed to give further evidence about COVID on 26 May.
What has been happening since then?
On 22 April, Downing Street officials briefed against Cummings, blaming him for the leaking of Johnson’s text messages to billionaire Sir James Dyson in which the PM promised the entrepreneur he would “fix” a tax issue for Dyson staff working to develop ventilators at the height of the coronavirus crisis last year.
Cummings hit back a day later, denying the claims and also sharing Johnson's "possibly illegal" plans "to have donors secretly pay for the renovation" of his Downing Street flat. The Electoral Commission is now investigating the Conservative Party.
Since then, Cummings has been increasingly active on his Twitter account, focusing on what he sees as Downing Street's COVID mismanagement in a hint of what will come at Wednesday's committee hearing.
In a blitz of posts over the past week, Cummings has:
blamed government secrecy over its COVID response for the “catastrophe” in spring last year
suggested vaccines could have been in use in the summer if greater risks were taken. The UK was the first country in the world to administer a jab, in December last year, and the rollout is considered one of the few successful aspects of its coronavirus response
claimed he has the "only copy of a crucial historical document from COVID decision-making". He later deleted this tweet
claimed all three lockdowns could have been avoided if the "right preparations" had been made, with "competent people in charge"
reiterated his claim that herd immunity, the idea enough people can become resistant to a disease through exposure to it, was an initial government tactic. This has been denied by home secretary Priti Patel, energy minister Anne-Marie Trevelyan and UK Health Security Agency chief executive Dr Jenny Harries. Yet in March last year, government Behavioural Insights Team leader Dr David Halpern and government chief scientific advisor Sir Patrick Vallance openly talked about herd immunity as a strategy
How damaging could Cummings's committee appearance be for Boris Johnson?
Clearly, it’s impossible to say without knowing what Cummings is going to tell the committee, or what documents he is going to share.
On a basic level, though, it’s questionable how much damage Cummings can really inflict on the PM, given his influential role as his chief adviser during the outbreak.
There's also his standing among the public.
He may have masterminded the Vote Leave campaign in the 2016 Brexit referendum, as well as Johnson’s commanding victory in the 2019 general election, but most people know him as the guy who drove to Barnard Castle to test his eyesight.
Cummings made that admission during an extraordinary Downing Street press conference, one year ago on Tuesday, in which he attempted to justify his lockdown trip from London to the North East.
Twelve months on, the Cummings scandal still appears to resonate with people. Amid Johnson’s own scandal surrounding the flat refurbishment, YouGov asked 2,835 Britons on 26 April who they were more inclined to believe.
While 46% said neither, 22% chose Johnson. Only 16% chose Cummings.
Johnson, on the other hand, has repeatedly evaded the consequences of political scandal during his career. The flat renovation row – which had been accelerated by Cummings's claims – is the latest example of this.
Since then, Johnson has celebrated an extraordinary by-election win in Hartlepool, while YouGov's monthly approval rating tracker had him on 48% on 10 May... his highest score since his ratings were damaged by news of Cummings's lockdown trip.
Watch: Dominic Cummings refuses to comment on Boris Johnson (from 19 May)