"God save the King", the male version of the royal anthem, was also sung during the ceremony for the first time in over 70 years.
Some 2,000 people attended the first religious ceremony of remembrance for Queen Elizabeth II at Paul's Cathedral on Friday.
Members of the public took part, as well as public figures like the Mayor of London, the Prime Minister and the leader of the Labour Party. However, no members of the royal family were present.
There were many words of affection for the late Queen, and there was a truly historic moment when the church sang "God Save the King" for the first time in 70 years.
Despite Charles III not being present, his speech, in which he vowed a lifetime of service, was broadcast to the audience.
"I have been brought up to cherish a sense of duty to others and to hold in the greatest respect the precious traditions, freedoms and responsibilities of our unique history and our system of parliamentary government.” Charles III said as he promised to uphold the constitutional principles of the UK.
Before his speech, King Charles III met with the newly elected Prime Minister, Liz Truss. The death of Queen Elizabeth II comes at a difficult time for Truss and the nation as they face an energy crisis and soaring inflation.