Boris Johnson was among the latest group of MPs to pledge allegiance to the King as the House of Commons met for the first time since the Queen's funeral.
The Conservative former prime minister was the 15th MP on Wednesday to take an oath of allegiance to Charles.
Mr Johnson spent time in the queue chatting with DUP MP Sammy Wilson (East Antrim) and Transport Secretary Anne-Marie Trevelyan.
Holding the King James Bible, Mr Johnson 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."
Ms Trevelyan was the first MP to swear in on Wednesday followed by Home Secretary Suella Braverman.
MPs are sworn in after each general election so they can take their seat, speak in debates, vote and receive a salary.
The wording of the oath means MPs have already pledged their allegiance to the heirs and successors of the Queen, meaning they do not have to do it again at this point.
A total of 31 MPs pledged their allegiance to Charles during the first swearing-in session.
Commons Speaker Sir Lindsay Hoyle opened proceedings by thanking parliamentary staff, members of the armed forces and others for their efforts during the Queen's lying-in-state and funeral.
He told MPs: "I also want to put on record my gratitude to all those who helped ensure events of the last 10 days or so have been managed with such dignity and brilliance, albeit in the saddest of circumstances.
"That includes, of course, many outside this House, including our armed services, the police and countless others.
"I want to say a very special thank you especially to all those parliamentary staff, including colleagues who volunteered to take on roles beyond their day jobs who contributed and you ensured that Parliament was able to play its part safely, respectfully and with pride, and so I am extremely grateful for all that has been done."
MPs can swear the oath or affirm throughout Wednesday, with Sir Lindsay also advising: "I remind members that swearing-in is recorded by the television cameras, anything said or done by members may appear on television or may be picked up on the microphones."
Normal business in the Commons will resume on Thursday.
