Britain's Royal Mint released a commemorative coin Thursday featuring portraits of Prince William and his bride-to-be, but critics said the results were far from lifelike.

Some critics say Kate Middleton, 28, appears plump in the face and lips and has bags under her eyes, while others suggest William looks more like former U.S. vice-president Al Gore.

Available in silver or gold, the £5 ($7.75 Cdn) coin — which costs £9.99 ($15.50) to buy — marks the April 29 wedding date for the second-in-line to the British throne.

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A commemorative coin to mark Prince William and Kate Middleton's engagement has sparked controversy over the likeness of the couple. ((Royal Mint/Associated Press))

"This coin is of historical importance. To get it so wrong seems ridiculous," Ingrid Seward of Majesty magazine told Britain's Sky News.

The Royal Mint said the coin was designed by its in-house engraving team and had gone though "a rigorous approval process."

The Queen and Prince William gave their consent to the design and staff had used photos of the couple to produce the images, it said in a release.

"The inspiration for the design came from photographs of the couple at a sporting event," the agency said.

Dickie Arbiter, a former royal spokesman, said it is often difficult to produce accurate images on a coin.

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"The Royal Mint has been recording historical events for over 1,100 years," said Dave Knight of the Royal Mint.

The coin is the latest official merchandise to celebrate the royal wedding. William's office has also already approved a souvenir tankard, plate and pill box that feature the couple's entwined initials, the prince's coronet emblem and the date of the wedding.