Senior MPs have pledged their allegiance to King Charles III in a rare Saturday Commons sitting.
Commons Speaker Sir Lindsay Hoyle was the first to do so.
He was followed by Father of the House, the longest serving male MP, Conservative Sir Peter Bottomley.
Then came the Mother of the House, the longest serving female MP, Labour’s Harriet Harman.
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New Prime Minister Liz Truss, who only gained the keys to Number 10 on Tuesday, followed them.
She said: “I swear by almighty God that I will be faithful and bear true allegiance to His Majesty King Charles, his heirs and successors, according to law, so help me God.”
Next were members of the Conservative whips’ office, Labour leader Sir Keir Starmer, Liberal Democrat leader Sir Ed Davey and the SNP’s Westminster leader Ian Blackford.
Plaid Cymru’s Westminster leader Liz Saville Roberts took an oath in both English and Welsh.
She was followed by former Conservative PM Theresa May and current Deputy PM Therese Coffey.
At the same time, senior members of the House of Lords, including Archbishop of Canterbury, the Most Reverend Justin Welby, also swore the oath of allegiance to the King.
Sir Lindsay said that “time constraints” meant only some MPs could take the oath or affirm on Saturday, but that further time to do so would be made available at a later date.
Every MP will have the option of taking an oath or affirming to the King when the commons returns after the period of national mourning – but they are not obliged to.
It is only the sixth time that the commons has sat on a Saturday since the Second World War.
The other times were:
• 2 September 1939 – for the outbreak of the Second World War
• 30 July 1949 – for summer adjournment debates
• 3 November 1956 – to discuss the Suez Crisis
• 3 April 1982 – to discuss the Falkland Islands invasion
• 19 October 2019 – to discuss Boris Johnson’s Brexit deal
Both the House of Commons and House of Lords also met from midday on Friday to allow for MPs and peers to pay their respects to the Queen following her death.
The Commons chamber was a sea of black as MPs stood for a minute’s silence before Ms Truss led Friday’s tributes, saying that the Queen was “one of the greatest leaders the world has ever known”.
She added: “As we meet today, we remember the pledge she made on her 21st birthday to dedicate her life to service. The whole House will agree, never has a promise been so completely fulfilled.”
Speaking for the first time since returning to the Conservative back benches earlier in the week, Boris Johnson said: “The fact that today we can say with such confidence, God save the King is a tribute to him, but above all, to Elizabeth the Great who worked so hard for the good of her country, not just now, but for generations to come.
“That is why we mourn her so deeply. And it is in the depths of our grief that we understand why we loved her so much.”
Sir Keir added: “The loss of our Queen robs this country of its still point, its greatest comfort at precisely the time we need those things most.
While former PM Mrs May said the Queen was “the most remarkable person I have ever met”.
The event was also littered with laughter and fond memories of the Queen who ruled for more than 70 years.
Parliament’s tributes followed an outpouring of grief from across the political spectrum as the world digested news of the Queen’s death at the age of 96.
MPs will continue paying tribute to the Queen this afternoon.