The King has enlisted the help of some of the UK's most special creatures to deliver a 100th birthday message to Sir David Attenborough. His Majesty was supported by a cast of stars from British nature to relay his handwritten congratulatory card from Balmoral Castle to London for the beloved naturalist.
In his note, the King said: "Dear David, my wife and I are delighted to learn that you will be celebrating your 100th birthday on May 8th and wanted to send you our warmest congratulations on such a special occasion. It is amazing to think that you and I have known one another for more than 60 years. Indeed, I believe we first met in 1958, almost a decade before the age of colour television and, of course, our paths have crossed many times since."
Writing in the card featuring a photo of the King and Queen on the front, he continued: "Over those decades, you have revealed the beauty and wonders of nature to audiences around the world in new and marvellous ways.
"In so doing, you have shared my determination to highlight the urgent need to protect and preserve this precious planet of ours, and all life on Earth, for future generations.
"Thank you then, for all that you have done, and on behalf of the whole nation, I wish you a very happy 100th birthday."
Sir David was set to be surprised with the video at a star-studded live tribute at the Royal Albert Hall on Friday, attended by Prince William.
The short film follows the journey of the royal's letter to Sir David, which initially gets thwarted by a fallen tree.
A roll call of heroic animals, including an eagle, a fox, a red squirrel and an otter, jump into action and traverse the British Isles to ensure that Sir David receives his royal dispatch.
To a tune from The King's Piper, the film begins with His Majesty donning an elephant-themed tie while penning his tribute to Sir David at Balmoral Castle's library last month, with photographs of Queen Elizabeth II in the background.
Her Majesty the Queen's dog Moley, who was adopted from Battersea Dogs and Cats Home, is seen scampering around his desk - which features two snowy owls to highlight the urgent need to protect and preserve the planet.
The King wistfully recounts a seven-decade friendship with the broadcast giant that began when the then nine-year-old Prince Charles visited the set of the BBC children's programme Zoo Quest in 1958 with his sister Princess Anne.
His Majesty goes on to acknowledge the enormous impact that Sir David's work has had in unveiling the beauty and wonder of the natural world to audiences across the globe.
A butler named Tony, who has worked for the Royal Household for over 30 years, begins the note's journey by carrying it on a silver salver to a waiting Land Rover.
But progress is suddenly halted.
To the tune of Take That's Greatest Day, a whimsical mission ensues as a border collie sheepdog named Flynn takes charge and sparks an epic handover involving several magical creatures.
From the Highlands to towns and waterways across Scotland and England, the card is carried, ferried, flown - and even wedged between the spines of a hedgehog - as it travels ever closer to its destination.
The journey concludes when the much-travelled envelope is gently delivered through the letterbox of Sir David's London home by a barn owl called Lily.
A Buckingham Palace spokesman said: "His Majesty was delighted to feature in this special tribute to a man who has shared his lifetime commitment to the natural world, and has followed each stage of the filming process with great interest.
"He was only sorry not to meet Lily the magical barn owl in person. Her Majesty was particularly touched that her mischievous Moley was invited to make a cameo appearance and was on hand with a ready selection of dog treats to help coax a willing performance on the day.
"The King and Queen send their warmest wishes to Sir David on his special night and hope he enjoys the resulting film as much as they enjoyed making it."
The Royal Albert Hall celebration, broadcast on BBC One, was hosted by Kirsty Young and included performances from musicians who have featured on Sir David's BBC Planet Earth TV series.
Dan Smith, frontman of Brit Awardwinning act Bastille, joined the BBC Concert Orchestra to perform their track Pompeii, which was featured in Planet Earth III, while Icelandic band
Sigur Ros played Hoppipolla, which was used in the promotion of Planet Earth and Planet Earth II.
The BBC Concert Orchestra performed the scores associated with some of the most unforgettable moments from Sir David's programmes, including the dramatic snakes and iguanas chase from Planet Earth II, and the powerful wave-washing orcas sequence from Frozen Planet II.
There was also music from British singer Sienna Spiro and Paraguayan harpist Francisco Yglesia, who will play the traditional Pajaro Campana - a piece that featured in Zoo Quest, Sir David's first wildlife programme.
Sir David has been "completely overwhelmed" with wishes from celebrities, environmental charities and animal welfare organisations who marked his milestone.
Former England footballer Sir David Beckham was among those to share an online post with the caption: "Happy 100th Birthday to our national treasure."
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