Two parties were held in No10 at a time of national mourning and with England under restrictions banning indoor mixing of households.
The monarch, 95, sat alone at the socially-distanced service at St George's Chapel in Windsor on 17 April and only 30 royals were able to attend Prince Philip's funeral in-person due to restrictions at the time.
WATCH: When have Prime Ministers had to apologise to the Queen?
The Prime Minister publicly apologised to the Queen as he faced the cameras on Tuesday at Finchley Memorial Hospital in north London.
"I deeply and bitterly regret that that happened," he said. "I can only renew my apologies both to Her Majesty and to the country for misjudgments that were made, and for which I take full responsibility."
It comes after Downing Street last week confirmed that an apology had been made to Buckingham Palace after news of the parties at No10 came to light.
Prime Minister Boris Johnson's official spokesman said last Friday: "It's deeply regrettable that this took place at a time of national mourning, and No10 has apologised to the Palace.
"You've heard from the Prime Minister this week, he's recognised No10 should be held to the highest standards and take responsibility for the things we did not get right. We have apologised to the Palace."
The Queen sat alone at her husband's funeral in April 2021
The Telegraph reported that two leaving events took place in No10 on 16 April, at which time indoor social gatherings were banned.
The Duke of Edinburgh passed away at the age of 99 on 9 April, with his funeral taking place on 17 April.
The Queen was accompanied by her lady-in-waiting, Lady Susan Hussey, as she travelled to the service, but she sat alone inside the chapel as she bid farewell to her husband of 73 years.
An inquiry into alleged government lockdown parties is being carried out by senior civil servant, Sue Gray.
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