Gold can be worth a hefty sum of money especially if it's by royalty. A rare gold coin commissioned by Britain's King Charles I has been sold for over $305,000 at an auction.

The rare item - produced between 1642 and 1644 by the king's Dutch designer Abraham Van Der Dort and worth $4 when it was minted - has become the most expensive item of legal tender ever sold in Britain.

Also known as a Triple Unite, the coin was created at Charles's request for new coinage.

However, the monarch later did not approve with Van Der Dort's designs and chose a different prototype for mass production, therefore making the coins unique.

Stephen Hill, the director of London's auction house A. H. Baldwin and Sons, where the coin was sold, says the particular example was a rare find.

He told Britain's Daily Mail newspaper, "For whatever reason he did not make another like it. This was the only one. It is unique. Other Triple Unites, made after that time, are rare but you can find them. The fact that this was the only prototype made by Van Der Dort makes it very special indeed."

The coin - which shows the king holding a sword on one side and an olive branch on the other - was bought by an anonymous telephone bidder. Ian Goldbart, of the auction house, added the coin generated great interest among collectors around the world because of its historical significance.

He said, "This is a truly magnificent, unique gold coin. It is of the highest importance in the development and history of engraving and minting for gold coinage of Charles I."