The King and Queen arrived at the Welsh Parliament on Thursday to loud chants from protestors.
As Charles, 77, and Camilla, 79, stepped out of their car at the Senedd, they were met with loud chants of "not my King" and "down, down, down with the Crown".
Protesters held placards which read "abolish the monarchy" and "down with the crown".
The chanting could be heard clearly as Charles and Camilla walked up the Senedd steps to greet First Minister Rhun ap Iorwerth and Huw Irranca-Davies, the Llywydd (presiding officer).
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However, the royal couple didn't appear to give the noisy shouts a second thought, continuing with the greetings as usual, as though nothing had happened.
Their welcome was otherwise warm and, as Their Majesties departed the Senedd after the opening of Parliament, they were met with heartfelt shouts of "We love you King Charles!" to which the monarch responded with a cheery wave.
The visit came as Charles's younger son, Prince Harry, made his first joint outing with his wife Meghan Markle since their return to the UK in August.
HELLO! previously revealed that the King and his son have not met in person since, though they are thought to have spoken over the phone.
Times the royals have been heckled and met with protests
The royal family often has to deal with being heckled on public outings, particularly by anti-monarchy protestors.
Grievances may include anti-monarchist chants, how much their security costs the taxpayer, and ongoing topics of scrutiny, such as Andrew Mountbatten-Windsor's friendship with Jeffrey Epstein.
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Anti-monarchy group Republic held banners reading "Stop the Reign" while chanting "not my King" and "not my Queen".
However, Kate remained perfectly composed and sent a cool glance in their direction.
Earlier this year, King Charles and Prince William were heckled on public engagements over Andrew after his name appeared in January's release of so-called Epstein files.
King Charles's speech during the Welsh Opening of Parliament
During his speech at the ceremonial opening of the Senedd, Charles hailed his "special connection" with Wales as he attended for the first time since becoming monarch.
He said on Thursday: "I have always felt immensely privileged, and proud, to have had such a special connection with Wales – with its language, its culture and its landscape – for so much of my life.
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"As you take forward your task of government, we know you will bear always in mind, and draw inspiration from, those shared strengths, as you work on behalf of the people of this most special corner of the Earth."
"Pob bendith ar eich gwaith er lles y wlad arbennig hon," he added in Welsh, meaning: "Heartfelt thanks for your work for the welfare and success of this special land."
Charles, Camilla and the Prince of Wales will visit Wales again next week to commemorate the 60th anniversary of the Aberfan tragedy.