The card, sent by Diana to Mervyn Wycherley, is inscribed: "Dear Mervyn, wishing you a very Happy Birthday, with much love from Diana, x"

It is among 27 letters, notes and cards all sent by Diana to Mr Wycherley in the 1980s and early 1990s, which are now expected to fetch a total of £8,000 at Reeman Dansie Auctions, in Colchester, on Monday, November 24.

The birthday card with the condoms illustration is tipped to sell for between £100 and £150.

Diana even took the trouble to write to Mr Wycherley while she was on her honeymoon, on the royal yacht, Britannia, and in that letter, dated August 13, 1981, which is expected to fetch between £1,000 and £1,500, she says: "Dear Mervyn, I did so want you to know how much we appreciated everything you did for us on Britannia.

"It has been a tremendous treat to have such delicious and exquisite food, even counting the rice pudding!

"How spoiling to know that that might always be the case....We only hope you enjoyed the cruise as much as the newlyweds and thanks to you our honeymoon was made – with endless gratitude from a couple of overweight Wales's – Diana."

In another note, Diana says: "To Mervie – please could I have a bacon sandwich for breakfast and a much needed rest from our friend the tomato!"

Diana was pregnant at the time with Prince William and during this pregnancy she developed a craving for bacon and tomato sandwiches.

This note could sell for between £100 and £150.

Mervyn Wycherley – who started as a junior chef with the Queen – became head chef to the Prince and Princess of Wales in 1981 and was later awarded a Royal Victorian Medal for his devotion.

When Charles and Diana split up, Mr Wycherley stayed with Diana until shortly before her death.