Llwynywermod, near Llandovery in Carmarthenshire, was bought for £1.2 million by the Duchy of Cornwall estate on behalf of the then prince in March 2007 after he spent 40 years searching for the right place.
The former coach house and farm buildings are at the centre of 192 acres of idyllic rolling countryside.
The Daily Telegraph said that since the Duchy of Cornwall was passed to Prince William, the King has been paying rent on Llwynywermod.
Buckingham Palace confirmed that the King gave notice to the Duchy earlier this year that he would be giving up the lease which is due to expire later in the summer.
The quoted royal sources who said the King remained “passionate” about Wales, but had decided to give up the property because it was “unlikely” he would be able to use it in the same way as before.
The original owner, William Williams in the 13th or 14th century, was related to Anne Boleyn.
The old house and the disintegrating concrete and corrugated iron farm buildings, where there was also an abandoned slurry pit, were restored by Welsh craftsmen using traditional methods and local materials.
Charles also planted climbers including Albertine roses, jasmine and honeysuckle up the walls.
Six of the English field maples which formed the avenue of trees at William and Kate’s 2011 wedding were later rehomed at the Welsh retreat.
The idea was Charles’s, and with William and Kate’s approval he set them in the soil at the front of the house, along a rustic wooden fence.
The prince has spoken of the “enduring landscape of Wales” and how “its mountains, patchworked fields and woods; its coastline, castles, villages and market towns” play a vital role in attracting visitors.
He told Visit Wales: “It certainly cast its spell on me a long time ago.”
William inherited a £23 million-a-year income from the Duchy of Cornwall.
As heir to the throne, the prince is entitled to the annual surplus generated by the Duchy’s vast portfolio of land, buildings and financial investments.
He has also taken charge of overseeing the management of the estate.
In 2021-2022, the annual Duchy income came to £23 million for Charles, then the Prince of Wales and now King.