The King appeared in great spirits today as he arrived at the Commando Training Centre Royal Marines at Lympstone in Devon.
Charles, 76, met with Royal Marine trainees and instructors, as well as families and veterans of the Corps.
In his role as Captain General Royal Marines, he presented the King’s Badge and a Green Beret to the best all-round member of the King’s Squad on completion of their Commando Training.
His Majesty also revisited some of the facilities where he trained as a helicopter pilot in 1974.
The Royal Marines are the amphibious troops of the Royal Navy, acknowledged as one of the world’s elite commando forces.
The Commando Training Centre - which is divided into three training wings - is the primary training centre for the Royal Marines.
On average, 1,300 recruits, 2,000 potential recruits and 400 potential Officers attend training courses every year. In addition, the Training Wings run upwards of 320 courses a year for around 2,000 students.
The King holds the title Captain General Royal Marines and is the Ceremonial Head of the Royal Marines, assuming the role in October 2022.
The King appeared in great spirits today as he arrived at the Commando Training Centre Royal Marines at Lympstone in Devon
The role was previously held by the late Duke of Edinburgh, before His Majesty’s Grandfather King George VI and Great Grandfather King George V who, in 1918, designated that the senior training squad should be known as the King’s Squad and the best all-round recruit awarded the King’s Badge.
It comes after the King celebrated turning 76 on Thursday by opening the first of his two new Coronation Food Hubs as the Royal Family wished him a happy birthday.
The monarch headed to Deptford in South London to formally unveil the first hub, tour the centre with London Mayor Sadiq Khan and attend a surplus food festival.
The King appeared in high spirits as he smiled and was given a kiss by a worker. Royal superfan John Loughrey stood with a card and bouquet of flower for Charles, who was accompanied by Sir Kenneth Olisa, the Lord Lieutenant of Greater London.
Pupils from Rye Oak Primary School in nearby Peckham led the singing of happy birthday for Charles, with six-year-old Zariah presenting the monarch with a card.
Project chairwoman Dame Martina Milburn, Baroness Louise Casey and other representatives of the charities involved also met Charles. Volunteers from the Felix Project, who will run the Deptford hub, waved flags and cheers as the King arrived.
Thursday is the first anniversary of the launch of his Coronation Food Project which aims to bridge the gap between food need and food waste amid the cost-of-living crisis.
His Majesty also revisited some of the facilities where he trained as a helicopter pilot in 1974 (pictured)
King Charles III, the then Prince of Wales, during 'familiarisation' training in 1974 at the Commando Training Centre Royal Marines
King Charles takes the salute during a visit to the Commando Training Centre Royal Marines
King Charles III, as Captain General Royal Marines, awards Marine Osian Stephens the King's Badge
The King awards Marine Joseph Ryan, the Commando Medal during a visit to the Commando Training Centre Royal Marines
King Charles III, the then Prince of Wales, in his flying overalls having landed his Wessex V Helicopter on the parade ground at the Commando Training Centre Royal Marines
King Charles III (fourth right), the then Prince of Wales, during 'familiarisation' training in 1974 at the Commando Training Centre Royal Marines
The King's engagement was a solo one - with Queen Camilla, who had hoped to join him, still recovering from a nasty chest infection. He later virtually opened a second hub in Knowsley, Merseyside - with three more hubs due open in the year ahead.
Earlier in the day, the monarchy's social media accounts posted a birthday message with a formal portrait of Charles in the White Drawing Room at Buckingham Palace .
Prince William and Kate's account shared an image of the relaxed-looking monarch wearing sunglasses and a garland during his royal tour to Samoa last month.
The photograph was taken as he opened The King's Garden at a museum in Apia, and the message read: 'Wishing a very Happy Birthday to His Majesty The King!'
Prime Minister Sir Keir Starmer also tweeted a message, saying: 'Sending His Majesty The King my very best wishes on his birthday today. Many happy returns.'