LONDON — Boris Johnson's former communication manager apologized to the royal family Friday for a lockdown-breaching staff party in Downing Street on the eve of Prince Philip's funeral last year.

Former Downing Street Director of Communications James Slack said in a statement that he apologized "unreservedly" for the April job-leaving party.

Spokesman Jamie Davies said Johnson's office is "deeply regrettable that this took place at a time of national mourning and No. 10 has apologized to the palace."

The Daily Telegraph reports that Downing Street staff drank, danced and socialized on April 16 last year. The next day the widowed Queen Elizabeth II sat alone in the church during her husband's funeral service to adhere to social distancing rules.

Johnson isn't alleged to have attended the leaving party, but it is the latest in a string of rule-breaking social events that are threatening to topple the British prime minister.

The apology from the prime minister's office comes just two days after Johnson admitted to attending a May 2020 "bring your own booze" party that was held at a Downing Street garden at the height of COVID-19 lockdowns in England.

Johnson admitted he attended the event Wednesday, though he said he had considered it a work event. He said he was there for about 25 minutes, according to CNN.

"I want to apologize…With hindsight, I should have sent everyone back inside," Johnson told lawmakers in the House of Commons earlier this week.