The royal family has postponed appointments 'which could distract or distract from the election campaign' after Rishi Sunak called a surprise general election for the summer.
Buckingham Palace said the King and Queen have sent their "sincerest apologies" to those affected after Charles agreed on Wednesday to the Prime Minister's request to dissolve Parliament for an election - for the first time in his government.
The King and Queen's 80th anniversary performances on D-Day in Portsmouth and Normandy in June are expected to go ahead as planned, but the announcement of a July 4 vote disrupted other events in the carefully planned upcoming royal diaries.
A Buckingham Palace spokesperson said: "Following the Prime Minister's statement this afternoon calling a general election, the Royal Family will, in line with normal procedure, postpone any appointments that could distract attention or distract from the election campaign.
"Their Majesties sincerely apologize to anyone who may be affected by this."
The Royal National Lifeboat Institution's garden party on Thursday, marking the lifesaving charity's 200th anniversary, is still going ahead, with thousands of guests set to descend on the palace.
Charles, who has only just returned to public duties following his cancer diagnosis, and Camilla will not attend the outdoor gathering, and never will.
But the King's public appearances for the rest of the week are now behind him - including a visit to Crewe on Friday to tour a Bentley factory and a community center that supports people struggling financially, and another, not yet publicly announced event that was due to happen elsewhere on Thursday.
It is clear that this step is not a blanket approach to future events, and arrangements will be assessed on a case-by-case basis.
There is no confirmation whether the upcoming Japanese state visit, which was previously postponed due to the pandemic, will still take place in June.
The sovereign does not vote and is a constitutional monarch who must remain politically neutral.
Charles could be a candidate for his third prime minister.
His first was Liz Truss - but her spell as president was the shortest in British history - and the king welcomed Mr Sunak as his second prime minister just six weeks after he took the throne.
Mr Sunak revealed that he had spoken to King earlier on Wednesday to inform him of his decision and that the King had agreed to the request to dissolve Parliament.
The palace said Charles met Mr Sunak in person at the royal residence in London on Wednesday afternoon, following Charles' engagement at the Prince's Trust Awards.
They spent about 15 minutes together in the king's private audience chamber, instead of their normal weekly meeting on Wednesday evenings.
Sunak is not expected to visit the King again on Wednesday.
The king, who is still undergoing treatment for cancer, has carried out a raft of engagements since resuming public appearances in April and now has a number of tasks ahead of him after the prime minister announced his plan to take the country to the polls to go.
Speaking at Downing Street, Mr Sunak said: "Earlier today I spoke to His Majesty the King to call for the dissolution of Parliament.
"The King has granted this request and general elections will take place on July 4."
The King hosted the winners of the Prince's Trust awards at the Palace in the afternoon, where TV star Declan Donnelly joked that his celebrity partner Anthony McPartlin was missing from the reception because he was breastfeeding his newborn.
The engagement went ahead as planned, without any change in timing, ending around 3:15 p.m.
The King is also due to hold a Privy Council meeting afterwards, but Buckingham Palace is yet to confirm whether this will go ahead.
In a statement, Downing Street said: "The Prime Minister has today asked His Majesty the King to declare the dissolution of Parliament. His Majesty has expressed his pleasure that he will comply with this request.
"Parliament will be postponed on Friday, May 24. The dissolution will take place on Thursday, May 30. The general election will take place on Thursday 4 July.
"The new parliament will be convened on Tuesday, July 9, with the first business being the election of the speaker and the swearing-in of members, and the state opening will take place on Wednesday, July 17."
Under the Dissolution and Calling of Parliament Act 2022, which repealed the Fixed Terms Parliament Act 2011, the Prime Minister can seek the monarch's permission to dissolve Parliament and call a general election at a time of his choosing.
The date of the dissolution will be set by a Royal Proclamation, issued by the King, on the advice of his Prime Minister, and timed so that election day can take place on the date chosen by Mr Sunak.
The 2022 law restored the practice of the monarch dissolving parliament at the request of the prime minister, without the need for a parliamentary vote on plans for elections.
There is no fixed number of days that must elapse between the announcement of an election and its dissolution.
Normally it takes a few days later before the Commons and Lords can deal with urgent business.
In previous times before 2011, the late Queen's agreement to dissolve Parliament meant she had to hold a meeting of the Privy Council to approve a royal proclamation which was signed and stamped with the Great Seal of the Empire.
The date of the dissolution of Parliament is statutorily set at 25 working days before the proposed election day, excluding weekends or public holidays falling within this period.
For July 4 elections, this is May 30.
Dissolution is the official term for the end of a parliament.
The day after the general election, it will be the King's duty to invite the leader of the party that has won the most seats in the House of Commons to become Prime Minister and form a government - one of the few remaining personal prerogatives of the sovereign. .
It was one of the Queen's last duties, just two days before she died, when she appointed Liz Truss as Prime Minister at Balmoral Castle.
It was the first time the Queen, who had mobility problems, had carried out the main duties at her Scottish retreat rather than at Buckingham Palace.
