Boris Johnson attended a boozy leaving do for one of his senior advisors when the country was in lockdown last January, reports say.
The Prime Minister went to the Downing Street gathering on January 14 2021 while Brits were ordered to stay at home.
This event was listed in Sue Gray's highly-anticipated - albeit partial - report into Downing Street parties but the details were redacted.
Some Downing Street staff who attended were said to have downed prosecco with the PM who is understood to have stayed for five minutes, the Guardian reports.
He even gave a speech and thanked staff for their hard work.
News of this leaving bash comes one day after Mr Johnson told MPs "I get it and I will fix it", in the Commons.
Making a statement after Ms Gray's report was published, the PM said: "Firstly, I want to say sorry - and I'm sorry for the things we simply didn't get right and also sorry for the way this matter has been handled.
"It's no use saying this or that was within the rules and it's no use saying people were working hard. This pandemic was hard for everyone."
The bash was held for a former senior policy advisor who is now working in the Department for Digital, Culture, Media and Sport.
England had just been plunged into its third lockdown when this leaving bash was held.
Weeks before, Mr Johnson cancelled Christmas for millions across the country.
More than 16 parties have been uncovered across Downing Street, Whitehall and Tory HQ during lockdown rules since the Mirror’s first revelations on December 1.
We first uncovered a Downing Street Christmas party on December 18, 2020, while indoor social gatherings in London were banned.
Later revelations included a party with a spread of food in the basement of Tory HQ, which was not included in Ms Gray’s report.
It also emerged staff in No10 brought a suitcase of wine in to leaving dos the night before Prince Philip’s funeral - prompting an apology to the Palace.
Downing Street staff held 'wine-time Fridays' throughout the pandemic with Boris Johnson regularly witnessing the gatherings, the Mirror revealed.
Mr Johnson was accused of misleading Parliament after claiming he had been “repeatedly assured” there was no party, only to admit his own attendance at one.
The PM confessed spending 25 minutes at an outdoor “bring your own booze” gathering on May 20, 2020, but claimed he thought it was a work event.
Police are investigating 12 separate gatherings - including four that Boris Johnson attended and one in the Prime Minister's Downing Street flat
Officers are also probing a so-called 'Abba party' in Boris and Carrie Johnson's flat - which Boris Johnson explicitly denied happened.
The Telegraph have since reported the PM was in the Downing Street flat at the same time of this music themed party.
Punishments for those who have broken the rules could be limited to fixed penalty notices - which might not be publicly disclosed.
Downing Street has said they will reveal if Boris Johnson is handed a fine for flouting Covid rules - in another U-turn.
The PM's official spokesman said: "Obviously we are aware of the significant public interest with regard to the Prime Minister and we would always look to provide what updates we can on him, specifically."
Asked if that meant No 10 would say if he was given a fixed penalty notice, the spokesman said: "Hypothetically, yes."
Ms Gray's damning nine-page update said "at least some" of the gatherings were "a serious failure to observe not just the high standards expected of those working at the heart of Government, but also of the standards expected of the entire British population at the time.
But her report was stripped of almost all details after the Met Police asked Ms Gray to make only "minimal reference" to the 12 gatherings it was probing.
The Whiltehall enforcer conceded: "I am extremely limited in what I can say about those events. It is not possible at present to provide a meaningful report setting out and analysing the extensive factual information I have been able to gather."
