The Queen's record reign commemorated with a new £50 coin

The Royal Mint will honour the Queen's record as the U.K.'s longest-reigning monarch by releasing a special £50 commemorative coin. Only 100,000 face-value coins will be produced, each featuring portraits of both the Queen and Britannia.

Royal mint engraver Jody Clark, who designed the fifth definitive portrait of the monarch to appear on circulating coins since her ascension to the throne in 1952, says it is an "honour" to have been selected to design the historic keepsake.

In honour of the Queen's record-reign, a commemorative £50 coin has been released.

The 33-year-old engraver said, "Having my portrait of the Queen selected for Britain's coinage was an incredible experience, but now, seeing the portrait combined with my Britannia design on the U.K.'s new £50 coin is a double honour."

The coins are available to buy on the Royal Mint's website with a limited number of 100,000 coins on offer. The face-value coin follows the release of a £20 commemorative coin marking Prince George's birth in 2013, and the £100 coin engraved with an image of Big Ben to ring in 2015.

The Queen became the longest-reigning monarch in British history on Sept. 9, having surpassed the record set by her great-great grandmother Queen Victoria. The monarch was inundated with congratulatory messages when she reached the milestone, which she said was "not one to which I have ever aspired."

The Queen became the U.K.'s longest-reigning monarch on Sept. 9, 2015.

While she was keen for celebrations of the day to remain low-key, she is set to mark another approaching milestone – her 90th birthday – in monumental style. Buckingham Palace has announced that four nights of birthday celebrations will be hosted in Windsor's Home Park, with the Queen confirmed to attend the final show on May 15.

The Queen, whose birthday is April 21, will also mark turning 90 with the biggest street party ever on The Mall in London on June 12. It was confirmed in July that 10,000 guests will be invited to the celebrations, set to be attended by the Queen and Prince Philip along with her grandsons princes William and Harry and other members of the Royal Family.

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