A Fortnum and Mason chocolate box on which the Prince of Wales and the Duchess of Cornwall scribbled "crude" jokes and drawings 30 years ago is being put up for auction.
The tin shows a picture of Mr Fortnum and Mr Mason delivering Christmas presents in a horse-drawn carriage.
But the Prince and the Duchess have drawn a pile of horse manure and a puddle under the horse and scribbled silly jokes about diarrhoea and yellow rivers.
Both the royals have signed the chocolate box which shows early evidence of their friendship in the late 1970s.
It is expected to fetch up to £600 when it is put up for auction at Ludlow, in Shropshire, later this year.
Richard Westwood-Brookes, of Mullock's Auctioneers, said: "This is clearly the product of a jovial evening between Charles and Camilla.
"As we now know today they were very much in love at this time and some of the comments are somewhat ribald."
Mr Westwood-Brookes said the box had originally been given to member of staff at Blenheim Palace before they acquired it for auction.
Charles and Camilla's signatures on the box have been cross-checked with other documents to make sure they are legitimate.
The Fortnum and Mason box was on sale in Christmas 1977 - three years after the Duchess married Andrew Parker Bowles.
Mr Westwood-Brookes has put an estimated price of £600 on the box but says the bidding could go a lot higher.