Boris Johnson is set to appear before the COVID-19 Inquiry, where he is expected to apologise for mistakes made during the pandemic - including over the government's speed at reacting to the outbreak.
It is likely to be uncomfortable for the former PM, who will be grilled for two days - Wednesday and Thursday - over his role in leading the government's coronavirus response during the early days of the pandemic.
Johnson's attitude to lockdowns, including his desire to protect the economy and ability to follow his own rules, are likely to be among the questions he will be posed.
How can I watch the COVID Inquiry live?
The inquiry is being livestreamed with a three-minute delay on YouTube.
Johnson's appearance will also likely be streamed on the BBC and Sky News.
What will Boris Johnson be asked about COVID and Partygate?
The COVID Inquiry is split into modules, and each module into parts. The current module of the COVID Inquiry is module 2, and Johnson will be asked questions about the government's response to coronavirus during the early days of the pandemic.
Uncomfortable questions likely to be put to the former prime minister include whether he took the threat of COVID seriously enough at the beginning of the pandemic.
A former official told the inquiry that he thought Johnson had asked during the early days of COVID: “Why are we destroying the economy for people who will die anyway soon?”
He is also likely to be asked about the Partygate scandal, which saw him break his own COVID lockdown rules with gatherings at Downing Street and has been extensively scrutinised by other hearings.
Johnson previously described the Partygate hearing as a "witch hunt", which eventually prompted his resignation as an MP.
He is also likely to be asked about claims by his former chief scientific adviser Patrick Vallance and former chief advisor Dominic Cummings that he did not fully understand the science behind COVID-19.
What will Johnson say at the COVID Inquiry?
The former prime minister is expected to concede that the government did not get everything right in the fight against coronavirus.
However, according to the BBC, he is also expected to say that the government did get "many of the big calls right".
He is expected to defend changing his mind on key issues during the pandemic, arguing that he was presented with lots of changing information in a short space of time.
Commentators have also pointed out that Johnson, who has been known to make political comebacks under the most dire of circumstances, may also be viewing the inquiry as an opportunity to manage some of the damage done to his reputation under the previous Partygate inquiry.
What power does the inquiry have?
Under the powers of the Inquiries Act 2005, inquiry chair Baroness Hallett has the power to compel documents and call witnesses to give evidence under oath.
Anyone who conceals a relevant document or prevents it from being given to the inquiry can be fined or imprisoned, with a maximum term of 51 weeks.
She is supported by a team of lawyers and civil servants, led by the inquiry counsel, solicitor and secretary.
The four inquiry modules that have so far been opened cover: resilience and preparedness; core UK decision-making and political governance; the impact of the pandemic on the healthcare system and vaccines and therapeutics.
More modules will be opening in the coming months, covering issues such as personal protective equipment, test and trace and health inequalities.
The hearing are predicted to continue until 2026, although interim reports are expected to be published before then.