A metal detectorist has found a Henry III gold coin minted 765 years ago.

The coin is expected to fetch more than £500,000 when it comes up for auction.

The piece is only one of eight known examples.

The last one was found 260 years ago.

A man with a metal detector found the gold coin near Hemyock in Devon.

He put it on Facebook not realising that it was incredibly rare.

However, expert Gregory Edmund from the coin dealer’s Spink spotted the coin.

Mr Edmund said:

“I immediately told the finder to take it down because you’re going to be inundated with every man and his dog to try trying to buy this off you for a fraction of what it’s worth”.

Mr Edmund and the finder took the coin to be assessed by the British Museum.

The finder, who doesn’t want to be named, said:

“The coin was found in an unappealing field and could quite easily have never been recovered.

“Now it is protected for future generations to enjoy, and it is truly humbling that I was its finder.

“My wish that day came true, and I just happened to be the fortunate one.

“I feel I have to apologise to all those other detectorists who search and dream.”

Because it is a single coin and not part of a hoard the finder is allowed to keep it.

It will be sold later this month (January) with an estimate of £400,000.