Harry, the Duke of Sussex, last saw his father in February 2024, shortly after it was announced that the King was undergoing treatment for an unspecified form of cancer.
Buckingham Palace confirmed that Charles, 76, had a private tea at Clarence House in London with his son on Wednesday.
The meeting between the two lasted 54 minutes.
Harry, 40, flew into the United Kingdom on Monday for a series of engagements, and earlier on Wednesday visited a research centre which specialises in improving treatment for victims with blast injuries.
Since Harry and his US wife Meghan moved to California in 2020 where they now live with their two children, they have been highly critical of the royal family and the institution in interviews, TV documentaries and Harry's autobiography Spare.
Harry had some particularly barbed comments for Charles and his elder brother, heir-to-the-throne Prince William, leading to a total breakdown in his relationship with his family.
But after losing a legal battle with the UK government over his security in May, Harry said he wanted a rapprochement.
"Of course some members of my family will never forgive me for writing a book. Of course they will never forgive me for lots of things. But you know ... I would love reconciliation with my family ... There's no point in continuing to fight anymore. And life is precious," he told the BBC.
"I don't know how much longer my father has. He won't speak to me because of this security stuff but it would be nice to reconcile."
Both Buckingham Palace and Harry's representatives had been tight-lipped ahead of the prince's visit to the UK about whether there would be a meeting with the King.
However, Charles' communications chief and Harry's media representatives were pictured in July at a secret meeting in London in what newspapers suggested might be the first steps towards a reconciliation.
Historian and author Anthony Seldon said mending their relationship was important for the monarchy and for both Charles and Harry as individuals.
"The King is the king but he's also a human being and a loving father," Seldon told Reuters.
"I think the rift will have caused both of them a lot of anguish. So if that can be healed, at least in part, now or subsequently, then that's all to the good."
with PA
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