The King officially marked the first year of his reign on Friday 8 September, as he took the day to remember his late mother, Queen Elizabeth II.
King Charles III issued his first statement as King 34 minutes after the late Queen's death was announced to the world.
He described his mother's passing as "a moment of the greatest sadness".
The late Queen's state funeral took place nine days later at Westminster Abbey, followed by a committal service at St George's Chapel in Windsor.
Since becoming King, Charles has undertaken engagements in 161 days, including travelling to all four nations of the UK and attending dozens of functions, according to PA News Agency.
As HELLO! marks the first year of Charles's reign, take a look back at some of his major milestones from the last 365 days
First Christmas broadcast
The King paid a touching tribute to his late mother in a pre-recorded message from St George's Chapel in Windsor, which aired on Christmas Day, as per tradition.
The monarch said: "I am standing here in this exquisite Chapel of St. George at Windsor Castle, so close to where my beloved mother, The late Queen, is laid to rest with my dear father."
It was just three months after the late Queen's death.
He continued: "I am reminded of the deeply touching letters, cards and messages which so many of you have sent my wife and myself and I cannot thank you enough for the love and sympathy you have shown our whole family.
"I am reminded of the deeply touching letters, cards and messages which so many of you have sent my wife and myself and I cannot thank you enough for the love and sympathy you have shown our whole family. Christmas is a particularly poignant time for all of us who have lost loved ones. We feel their absence at every familiar turn of the season and remember them in each cherished tradition."
First State Visit
The King's inaugural state visit to Germany in March was dubbed a success and saw Charles deliver the first speech by a British monarch – mostly in German - during a session of the Bundestag.
A trip to France before their German leg was set to become Charles and Camilla's first official state visit, but the trip was shelved at the last minute following riots across the country over pension reforms.
The couple will now carry out their rescheduled state visit to Paris and Bordeaux from 20 to 22 September.
First Easter at Windsor
The King and Queen led the royals at the Easter Sunday church service in Windsor, with appearances from some of the youngest members of the family, including the Prince and Princess of Wales's three children and Mike and Zara Tindall's daughters.
First official portrait as King and Queen
A week before the coronation, Buckingham Palace released the first official portraits of Charles and Camilla to mark their reign.
The images were taken in the Palace's blue drawing room by their wedding photographer Hugo Burnand, with one showing the King and Queen, coordinating in blue and standing side by side in front of a portrait of King George V painted shortly after his coronation in June 1911.
Two further images also showed Charles and Camilla seated individually.
The King and Queen's joint coronation took place at Westminster Abbey in May, in front of 2,500-strong congregation, while over 20 million Brits watched the ceremony on TV.
See all of the highlights from the day in the clip below…
First Trooping the Colour
It was the first time a monarch has ridden on horseback since the late Queen Elizabeth II rode on her beloved horse, Burmese, in 1986.
Senior working royals joined the King on the palace balcony to watch the flypast.
First summer at Balmoral
Among their guests were the Prince and Princess of Wales, the Duke and Duchess of Edinburgh, the Princess Royal and Vice Admiral Sir Timothy Laurence and the Duke of York.
The pair also attended their first Braemar Gathering Highland Games of their reign, and as tradition, they hosted Prime Minister Rishi Sunak and Akshata Murthy.