The special way Prince William will mark his 40th birthday this year

On January 9, Kate Middleton marked her 40th birthday with a series of portraits making subtle reference to the Queen and Princess Diana.

Now, her husband Prince William is about to reach that milestone too, on 21 June.

And in honour of the Duke of Cambridge's upcoming birthday, we've learned that he's due to receive a special gift, too.

The Royal Mint, entrusted by Her Majesty's Treasury to create official coinage for the United Kingdom, unveiled a £5 coin engraved with the duke's portrait.

It also features his royal cypher, with the letter W and the number 40, and is edged with an inscription that reads: 'HRH The Duke of Cambridge'.

This design marks the first time Prince William will appear alone on an official coin – he appeared on a £5 coin alongside then bride-to-be Middleton after their engagement and ahead of their Westminster Abbey wedding in 2011.

His and Middleton's coin was inspired by photographs of the couple at sporting events.

This time around, designer and engraver Thomas T Docherty created Prince William's portrait, but an image of The Queen, designed by Jody Clark, will appear on the other side of the coin.

As well as the £5 coin, a limited edition souvenir two-coin set will be released, with a 0.25oz gold celebration coin and a 1982 sovereign coin that marks the year Prince William was born.

A limited edition coin comprising of 5oz of fine gold quality, complete with laser technology for a 'high relief finish', will also be included in the collection, giving the duke's portrait a magnified 3D appearance.

Docherty said of the coin: "The design strikes a balance between the fresh energy of His Royal Highness being a young dad with the ceremonial nature of his royal position.

"A three-quarter angle of the portrait creates a more dynamic portrait rather than a traditional side-on profile.

"I used certain clay sculpting techniques on a digital platform to achieve the style needed for the design, to translate effectively from two to three dimensions."

Clare Maclennan, director of commemorative coin at the Royal Mint, said "the elegant design" nods "to the maturity and grace of the prince who has become a senior member of the royal family, a devoted husband and a loving father of three, through the eyes of the world".

At the time of Middleton's 4oth birthday portraits being newly released, Italian photographer Paolo Roversi revealed that the duchess gave him mid-19th century artwork from the likes of Dante Gabriel Rossetti and Sir David Coyle Burne-Jones "to give me inspiration".

The portraits included two black and white photos of her wearing two graceful gowns, and a coloured picture of her in a scarlet red dress, all designed by British fashion house Alexander McQueen.

They are due to appear in the National Portrait Gallery as part of a permanent collection when it reopens in 2023.

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