The design for an official commemorative coin marking Prince William and Kate Middleton’s engagement has been unveiled – but royal fans may have trouble recognising the couple.

The prince and his bride-to-be are featured on one side of the £5 collector’s piece being produced by the Royal Mint.

An image that bares some likeness to Prince William is shown in profile but Miss Middleton is face on and appears older and to have gained weight.

The coin was designed by the Royal Mint’s in-house engraving team and has the Queen in profile on the reverse.

The piece is the first royal engagement coin produced by the Royal Mint and was approved by the Queen and Prince William.

A Royal Mint spokesman said: “The inspiration for the design came from photographs of the couple at a sporting event – the play on the traditional portrait is that Prince William is seen in profile, alluding to his royal status.” When asked about Ms Middleton’s likeness a spokesman stressed that the design “does go though a rigorous approval process”. Many commemorative medals and coins have been created by the Royal Mint in honour of the monarchy during its 1,100-year history.

When Prince William’s father the Prince of Wales married Lady Diana Spencer in July 1981 the event was marked by a coin showing the couple in profile with the Queen’s image on the reverse.

Dave Knight, the Royal Mint’s director of commemorative coin, said: “The Royal Mint has been recording historical events for over 1,100 years and we’re fortunate to be in a role that allows us to add to that legacy.

“The £5 Alderney coin we have designed is a wonderful way to celebrate and remember the start of Prince William and Catherine Middleton’s life together.”

The couple will marry in April at Westminster Abbey.

The coin can be ordered on the Royal Mint’s website and is available in a number of metals from cupro-nickel, costing £9.99, to 22-carat gold priced at £1,550.