The King made his first public appearance on Friday following Buckingham Palace's confirmation that Charles's youngest son, Prince Harry, will attend his coronation on 6 May.
The monarch, 74, inspected the 200th Royal Military Academy Sandhurst's Sovereign's Parade, presenting the new Colours and Sovereign's Banner to the receiving Ensigns.
Charles was dressed in full military uniform for his engagement, where he gave an address and presented the prize winners' awards, including the Sword of Honour.
In his speech, the King said: "Speaking as a father of two alumni of this Academy who remembers their passing out parades, I know they will be full of immense pride in witnessing you on parade."
SEE: Prince Archie is Prince Harry's mini-me in beanie hat
© GettyThe late Queen attended the Sovereign's parade at the Royal Military Academy Sandhurst twice in 2006 to see her grandsons Prince William and Prince Harry graduate.
Charles joked: "Having attended – and survived! – two of the other Military Academies 50 years ago, I think I have some idea of the challenges which are inherent in military training.
"I have experienced the nerves, the exhaustion – even the self-doubt – but, despite such recollections, it is the lifelong friendships which are forged through shared hardship, and the humour that you find in the darkest hours of the coldest, wettest nights, which remain with you."
© GettyThe Parade marks completion of 44 weeks of intensive training for the Officer Cadets, all of whom will hold His Majesty's Commission as of midnight on the day of the parade.
The King's appearance comes after the palace confirmed in a statement on Wednesday: "Buckingham Palace is pleased to confirm that the Duke of Sussex will attend the Coronation Service at Westminster Abbey on 6th May.
"The Duchess of Sussex will remain in California with Prince Archie and Princess Lilibet."
While no reason was given for Meghan's absence, Archie's fourth birthday coincides with his grandfather's coronation and that is thought to be a key reason behind the decision. Meanwhile, Charles's eldest grandchild, Prince George, has been given a starring role at the ceremony...
It will mark the first time Harry has been reunited with his family since the late Queen Elizabeth's state funeral last September.
The Duke has spoken widely about his fraught relationship with the royals, including in his and Meghan's Netflix docuseries and his memoir, Spare, which was published in January. Most memorably he wrote about his fallout with Prince William, though their fraternal discord pales into insignificance compared with these six nasty royal brother fallouts from British history.
LISTEN: Want to hear more about the royal family? Check out the best of 'A Right Royal Podcast'
Make sure you never miss a royal story! Sign up to The Royal Explainer newsletter to receive your weekly dose of royal features and other exclusive content straight to your inbox.
