That announcement is just one of the ways that Charles will seek to play his part as a unifying head of state during the election, without violating a constitutional ban on interfering in politics. While the king's role in government is largely ceremonial, it's bound up by traditions that embody the way royal powers were gradually transferred to Parliament over the last 800 years.
Here's a look at the monarch's role in the run up to the election, including a few dos and don'ts.
The decision to call an election was entirely Sunak's. But before he could do so, the king had to grant permission to dissolve Parliament early.
Technically, the king still has the power to refuse a dissolution request if he believes an election would be detrimental to the nation. But the last time this happened was in 1835.
Ignoring that precedent "would expose the monarch to allegations of political interference of an undemocratic nature, even if the intention of the refusal was to preserve the good functioning of democracy," according to the Institute for Government, an independent think tank.
The current session of Parliament will be "prorogued," or ended, on Friday based on an order that Charles approved during a meeting of the Privy Council on Thursday at Buckingham Palace.
The king won't attend the formal end of the session, a ceremonial affair where the speaker of the House of Commons and other members of Parliament will troop into the House of Lords to hear a speech written by the government.
The royal family is barred by law and tradition from interfering in politics at any time, but ensuring that those rules are strictly followed is even more important during an election.
That means the royals can't campaign for candidates, endorse policies, or even let their political preferences be known.
Buckingham Palace spelled it out soon after Sunak's announcement, announcing that members of the royal family would postpone all engagements that "may appear to divert attention or distract from the election campaign.''
That meant the king on Friday ditched trips to a Bentley car factory and a community center helping people who are struggling financially.
Well, some things are above reproach.
The king and queen still plan to attend ceremonies marking the 80th anniversary of D-Day on June 6.
Other engagements will be examined on a case-by-case basis, the palace said.
One of the modern monarchy's primary roles is to provide a unifying figurehead who is seen as above politics and can provide a sense of stability in difficult times.
This is the first general election of Charles' reign. His mother, Queen Elizabeth II, oversaw 21 during her 70 years on the throne.
George Gross, a royal expert at King's College London, said elections are by definition moments of turbulence in which people look to the monarchy for continuity.
"There is ... a power vacuum in political terms. Power is now handed back to the British people, and they will review the offering over the next six weeks,'' Gross said. "So what that means, though, is that the head of state has a new role. Or rather, (the) key role of stability and continuity comes to the fore. Now, (the royals) cannot be political in any way."