King Charles used his first speech to a foreign leader to signal his monarchy will tackle the legacy of colonialism.
Speaking before South African President Cyril Ramaphosa, he said aspects of the relationship between his country and the UK "provoked profound sorrow".
His Majesty called for future cooperation between the two nations.
He also said his late mother the Queen “always talked warmly of her return to your country” and even revealed former President Nelson Mandela's nickname for her.
Charles has continued to push to keep the Commonwealth unified as some member states are pressured to dump the monarchy completely.
As Prince of Wales, last year he condemned the "appalling atrocity of slavery, which forever stains our history" during a speech in Barbados.
The Caribbean island nation had broke ties with the Royal Family to become a republic.
Earlier this year, Charles also told Commonwealth leaders: "I cannot describe the depths of my personal sorrow at the suffering of so many as I continue to deepen my own understanding of slavery's enduring impact."
Speaking last night during a state banquet at Buckingham Palace, he assured he was committed to ensuring Britain acknowledges the "wrongs which have shaped our past".
The event was in honour of President Ramaphosa, who is on a two-day state visit.
King Charles said: "While there are elements of that history which provoke profound sorrow, it is essential that we seek to understand them.
"As I said to Commonwealth leaders earlier this year, we must acknowledge the wrongs which have shaped our past if we are to unlock the power of our common future.
He continued: "South Africa, like the Commonwealth, has always been a part of my life.
"The late Queen had the great pleasure of hosting Presidents Mandela, Mbeki and Zuma for State Visits to the United Kingdom, at all of which I was present.
"On each of those occasions, she expressed her admiration for your country and its people, its vibrancy, natural beauty and diversity.
"And she always talked warmly of her return to your country in 1995, as the guest of President Mandela, after the momentous events - driven from within South Africa and supported by so many around the world, including here in the United Kingdom - that brought democracy to your country."
The audience of 163 - which included Prince William and Princess Kate, as well as senior politicians - laughed when he added: "During one of my own visits to South Africa, in 1997, President Mandela told me that he had conferred on my mother a special name – Motlalepula, meaning 'to come with rain'.
"I have been reassured that this was a mark of the particular affection President Mandela felt for the Queen... rather than a remark on the British habit of taking our weather with us!"
Having opened his speech with the word "welcome" in several languages of South Africa, he ended by saying: "Nkosi Sikelel' iAfrika!"
