For the second time in two days, the sound of a gun salute reverberated around the Co Down village.
But while Friday’s 96-round salute was in memory of the late Queen, Saturday’s 21-gun salute marked the reign of a new King.
The union flag on top of the castle was temporarily moved to the top of the mast.
Outside the gates, hundreds of people had gathered. A lone piper could be heard playing the God Save The King and Abide With Me.
Several sash-wearing members of the Orange Order were also in attendance at the Co Down castle the moment Charles was proclaimed king at a ceremony in St James’s Palace.
The sea of floral tributes at the gates of Hillsborough Castle continues to grow, with bouquets and tributes now carpeting much of the tarmac and grass in the front area.
The public are being invited to come and pay their respects, but a significant security operation is under way in the village, with traffic restrictions and a shuttle bus service to take people to and from the castle.
Among those who came was Jennifer Crossland from Co Down, who said she felt compelled to come and pay her respects.
She said: “It was all such a big shock for everybody.
“The Queen was always there and this was her place to come to in Northern Ireland.
“It meant a lot to people here that she did come here so often.
“I was watching the news on Thursday when it was announced.
I have watched them all over the years, it is hard not to feel some sort of connection with the royal family
“I just felt this strange feeling, I just couldn’t believe it.
“It makes you remember all the people you have lost yourself and how death comes to us all.
“I once shook Prince William and Kate’s hand, when they came here after they got engaged. I spoke to Edward at the Balmoral Show.
“I have watched them all over the years, it is hard not to feel some sort of connection with the royal family.”
Books of condolence have been opened at locations across Northern Ireland following the death of the Queen and a number of sporting and public event this weekend have been cancelled.
More floral tributes were left on Saturday at the site of a mural of the Queen on Belfast’s Shankill Road and at CS Lewis Square in the east of the city.
Attention will return to Hillsborough on Sunday for the reading of the Accession Proclamation at the castle – at the same time as it is read in Edinburgh and Cardiff.
Later in the day the High Sheriff of Belfast John Hussey will don ceremonial robes when the proclamation is re-read at Belfast City Hall before a special meeting of the council to pay tribute to the Queen.
MLAs will return to Stormont on Monday to pay their tributes.