Looking back at the late Queen's legacy as he led the royal family's tributes on social media, the monarch said: "In marking the first anniversary of Her late Majesty's death and my Accession, we recall with great affection her long life, devoted service and all she meant to so many of us.
"I am deeply grateful, too, for the love and support that has been shown to my wife and myself during this year as we do our utmost to be of service to you all. Charles R."
Buckingham Palace has also shared an image of the late Queen, chosen by His Majesty to mark the anniversary.
The image shows Her Late Majesty captured by photographer Cecil Beaton at her official London residence, as part of an official sitting on 16 October 1968. Elizabeth II was seen wearing her Garter robes and the diamond Vladimir tiara with its pearl setting.
The photograph has not been released before now but it was first shown at the National Portrait Gallery between November 1968 and March 1969, as part of its first photographic exhibition ‘Beaton Portraits 1928-68’.
This was also the first retrospective of the work of a living photographer in a British national museum.
Beaton first photographed Her late Majesty in 1942. He photographed Her Late Majesty and many other members of the royal family across the decades but the 1968 sitting was their last sitting together.
His Majesty and the Queen are spending this poignant milestone privately at Balmoral, the former monarch's beloved summer home in the Highlands and where she passed away on 8 September last year. The King and Queen will head to Crathie Kirk for private memorial prayers alongside a very small number of Balmoral guests.
The Prince and Princess of Wales paid their own respects on social media, saying how much they "missed" the late Queen. They wrote: "Today we remember the extraordinary life and legacy of Her Late Majesty Queen Elizabeth. We all miss you. W & C."
Alongside the heartwarming post, the royal couple shared a series of images including one showing the late monarch with her grandchildren Lady Louise Windsor and the Earl of Wessex, and great-grandchildren Savannah and Isla Phillips, Mia, Lena and Lucas Tindall and Prince George, Princess Charlotte and Prince Louis.
The image was taken by the Princess of Wales during the royal family's annual summer holiday at Balmoral in 2022.
Princess Eugenie went on to release an unseen image with her late grandmother, and remarked: "Thinking of you today. Missing you so much but remembering what a life of service, love and dedication to everyone and to your family, who loved you so very much."
Princess Anne's son-in-law, Mike Tindall, also honoured the late Queen with a video showing the photos of her from birth up until her later years.
Prime Minister Rishi Sunak said the late Queen had wisdom, grace and a "sharp wit" in his tribute. He also expressed his gratitude for her service and "extraordinary life of duty and dedication" continues to grow, a year on from her death.
The Prime Minister said he treasured his memories of meeting the then-monarch, particularly his private audience before presenting his first Budget as chancellor in 2020.
"With the perspective of a year, the scale of Her Late Majesty's service only seems greater," he said. "Her devotion to the nations of the United Kingdom and the Commonwealth only seems deeper. And our gratitude for such an extraordinary life of duty and dedication only continues to grow.
"I treasure my memories of those occasions when I met Her Late Majesty, in particular the private audience I had with her at Buckingham Palace before presenting my first Budget as chancellor. I was struck by her wisdom, by her incredible warmth and grace, but also her sharp wit.
"People across the UK – whether they had the good fortune to meet Her Late Majesty or not – will be reflecting today on what she meant to them and the example she set for us all. We will cherish those memories."
The Prince and Princess of Wales also paid tribute to the late Queen as they spent Friday in St Davids in Pembrokeshire, where their itinerary included a poignant visit to the cathedral, which the late Queen herself visited several times.
"A moment of reflection at St Davids Cathedral honouring Her Late Majesty and all that she did for communities like this around the UK, the Commonwealth and the world," a post on their social media account read.
Queen Elizabeth II was the first British monarch in history to reach her Platinum Jubilee, and she also became the longest-reigning still-serving monarch in the world.
A year ago on Friday, Queen Elizabeth II was at Balmoral Castle in Scotland where she had been enjoying her annual summer holiday. However, fears for her health dramatically escalated on 8 September 2022 when Buckingham Palace announced the monarch was under medical supervision at her Aberdeenshire residence and her doctors were concerned.
Just two days before, on 6 September, she had been carrying out official duties, appointing Liz Truss as the prime minister. The late Queen died at 3.10pm, her death certificate later revealed, with the cause listed as "old age". News of her death and the accession of Charles as King was announced to the world by Buckingham Palace at 6.30pm that evening.
Last week, the Government announced details of a new memorial to our longest-reigning monarch after people were invited to submit ideas for a fitting tribute.
It will be in addition to existing legacy projects, such as the Queen's Green Canopy tree-planting initiative, the Royal Yacht Britannia in Edinburgh, now a popular tourist attraction, the London Underground's Elizabeth Line, and new statues of Elizabeth and her husband the Duke of Edinburgh at the Royal Albert Hall in London.
Plans for a permanent memorial to the late Queen will be unveiled in 2026 to mark what would have been Elizabeth II's centenary year.
In the first episode of HELLO!'s A Right Royal Podcast, writer and broadcaster Gyles Brandreth and photographer Julian Calder share their favourite memoires of the late Queen. Listen here...