This coin with the same story was for sale on EBay several times a couple of years ago, and featured on this site. It subsequently appeared with hype for sale via a conventional South Wales auction house (Dragon Auctions, or some similar name). After I sent them links to his EBay sale attempts, and to discussion on this forum , they sent me a pleasant email and withdrew the coin from sale. The story is of course total tosh, it is a modern Chinese replica, though he possibly paid too much for it himself if he did indeed buy it in Caerphilly and was taken in by the vendors stated provenance.
Jerry