In a phone call with Wales' first minister, the prince is said to have acknowledged his and the princess's deep affection for Wales.
"Today, I am proud to create him Prince of Wales, Tywysog Cymru," said the King, who held the title for 64 years, as quoted by the BBC.
Previously, the title was carried by Charles when Queen Elizabeth II was still alive.
The King was only 20 years old when he was crowned Prince of Wales in a ceremony at Caernarfon Castle, Gwynedd, in 1969.
"As my heir, William is currently taking on a Scottish title that means a lot to me," said The King