King Charles had pledged allegiance to his mother late Queen Elizabeth II after he was crowned as Prince of Wales at Caernarfon Castle in July 1969.
He pledged allegiance with the words: "I, Charles, Prince of Wales, do become your liege man of life and limb."
King Charles III spent time learning Welsh at university before he was crowned in a televised ceremony when he was 20.
During the elaborate investiture ceremony, the queen placed a coronet on Charles´s head and helped arrange robes around his shoulders.
Meanwhile, after Charles became king, heir to throne Prince William has inherited title of the Prince of Wales.
William, and his wife, Kate Middleton on Tuesday made their first visit to Wales since becoming the new Prince and Princess of Wales.
He inherited the title on the death of his grandmother, Queen Elizabeth II, when his father -- the previous prince of Wales -- became king.
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The two recently welcomed their first child to the world earlier this year in May