The King is to take part in the Trooping the Colour ceremony but will inspect the soldiers from a carriage rather than on horseback, it is understood.
Charles has recently returned to public-facing duties while still receiving treatment for an undisclosed form of cancer and will now take part in one of the highlights of the royal calendar.
But it is unclear whether the Princess of Wales, who is undergoing chemotherapy after a cancer diagnosis, will attend.
The celebration, which traditionally involves the royal family gathering on the balcony of Buckingham Palace after a display of pomp and military pageantry, will be held on June 15.
During the ceremony, held on Horse Guards Parade in Whitehall, it is understood the King will carry out the review of the Guardsmen and officers from an Ascot Landau carriage with the Queen.
The change from last year’s ceremony, where Charles inspected the troops on horseback, reflects earlier Buckingham Palace briefings where it was highlighted that each engagement by the King would be reviewed and adaptations made when advised by doctors.
The King had been carrying out a busy programme of engagements since it was announced just over four weeks ago would be returning to public facing duties.
Rishi Sunak’s decision last week to call a surprise summer General Election has meant the monarchy has postponed any engagements “which may appear to divert attention or distract from the election campaign”.
Charles is likely to travel by carriage with the Queen during the traditional procession to and from Horse Guards Parade, and is expected to watch the Trooping ceremony seated on a dais with the Queen, rather than on horseback.
Kate missed a Trooping rehearsal held earlier involving almost a thousand soldiers and around 240 horses from the Household Division, and staged in front of an audience of more than 1,000 people on Horse Guards Parade.
She was represented by Lieutenant Colonel James Shaw, Brigade Major of the Household Division, who designed this year’s spectacle and acted as the chief inspecting officer of the day in the princess’ absence.
In the coming days, the troops will carry out further rehearsals, The Major General’s Review on Saturday, The Colonel’s Review on June 8 before Trooping the Colour on June 15 – a ceremony which has marked the official birthday of the British sovereign for more than 260 years.
The colour which will be “trooped” past the massed ranks of Guardsmen and officer will be from Number 9 Company, Irish Guards.
Republic, the anti-monarchy group, has said it will stage the latest in a string of protests near Buckingham Palace on the day of Trooping the Colour.
Graham Smith, Republic’s chief executive officer, said: “Rather than see royals wear uniforms, rank and medals they’ve not earned, let’s put real military personnel front and centre.
“Instead of celebrating this undemocratic institution, let’s celebrate the people of this great country.”