A never-before-seen letter written by Princess Diana in June, 1989 is set to go under the hammer.
Sure to be a prized addition to any royal fanatic's collection, the heartfelt note offers rare insight into the touching celebration the late royal threw for Prince William's seventh birthday party.
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The thank you letter sees Princess Diana express her gratitude for Sergeant Plumb of Scotland Yard's Special Escort Group after he organised a motorcycle display for the big day.
Written on official Kensington Palace paper, the note reads: "Dear Sgt Plumb, it was so very kind of you and your team to have come here today on William's birthday."
"I cannot begin to tell you what pleasure the display gave to all those little people and their mothers!"
William George Auctions
The note written on 21 June, 1989, has now gone up for auction in the UK and includes Princess Diana's signature.
Adding to its sentimental value, both Princes William and Harry - then aged seven and four - also added their monikers to the bottom of the message.
A second letter written by Princess Diana's lady-in-waiting, Ann Beckwith-Smith, is also included in the auction bundle.
The note reads: "The Princess of Wales was enormously grateful to Sergeant Plumb and his team for ensuring that Prince William's seventh birthday was such a very special occasion and the display was enjoyed by grown-ups and children alike."
"Her Royal Highness was particularly grateful to the 'team' for being able to fit this is on a day already full of official engagements, which was not helped by the rail, underground and bus strike," she continued.
"It was greatly appreciated and I would be grateful if special thanks could be passed to all concerned, but especially Sergeant Plumb."
The highest bid currently stands at £7,500 (approximately $14,695).