A note in which the Queen Mother asked her aide to pack gin and Dubonnet has sold for £16,000 - well over the expected £3,000.
It was among the sought-after items in the collection of royal letters, photographs and artefacts auctioned on Saturday for a total of £444,634.
The items were discovered after the death of former royal servant William Tallon, known as Backstairs Billy.
He was in service for 52 years, and was a favourite of the Queen Mother.
The hand-written note, which sparked a telephone bidding war, asked for an outdoor lunch, with the added request: "I think that I will take two small bottles of Dubonnet and gin with me this morning, in case it is needed."
Backstairs Billy's cousin talks about the 'lovely man'
It took auctioneer James Grinter, of Reeman Dansie in Colchester, Essex, 10 and a half hours to sell the 700 lots.
About 400 people packed into the auction room, with another 1,000 placing bids by telephone and the internet.
It was thought that the collection could fetch at least £250,000. But with many items fetching higher prices than expected, the final total was almost double that.
A portrait of the Queen Mother, a miniature of a painting owned by the royal family, fetched the highest price of £30,000.
Solicitor Stephen Lansley, the executor of the will, said the beneficiaries, including a charity, would be announced in a fortnight.
Also popular was a letter to Mr Tallon from Princess Diana after the birth of Prince William.
Mr Tallon kept all the correspondence he received from the royals
She wrote: "We are not sure at the moment what has hit us, except a very strong pair of lungs."
That sold for £5,000 to a telephone bidder. Another seven letters she penned made a combined £15,000.
The collection paints a vivid picture of Mr Tallon's life as a royal insider. He joined the household aged 15, and kept every thank-you letter, Christmas card and invitation he received.
He never spoke publicly about the royals, and turned down requests to write a book or be interviewed. He died last November aged 72.
Janet Canon, of Reeman Dansie, said bidders had flown in from overseas, particularly from the United States and Canada.
A Buckingham Palace spokesman would not comment on the sale.
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