Prince Charles and Lady Diana Spencer wed in a globally broadcasted wedding 40 years ago.

On July 29, 1981, the chosen guests of their special day were treated to an extravagant slice from a five-tier wedding fruit cake, which was made by Dave Avery, head baker with the Royal Navy.

Along with their wedding cake, there were 22 others baked and sent out – including one that was made for Clarence House staff to enjoy.

One leftover slice of cake is going under the hammer in the UK and is expected to sell for £500 ($950).

The piece of cake, weighing in at 800g was given to Moyra Smith, a member of the Queen Mother’s household at Clarence House.

She used glad wrap to preserve the topping.

Mrs Smith kept the piece of history wrapped and stored in a floral cake tin.

She topped it with a handwritten label reminding anyone to “handle with care”.

The label was signed by Mrs Smith and dated 27 July, 1981.

Her family sold the piece of cake to a collector in 2008 but it has now found its way back onto the auction block, on their 40th wedding anniversary.

The cake features white icing, and a 3D sugared image of the royal coat-of-arms coloured in gold, red, blue, and silver.

It also has a small silver horseshoe and leaf spray.

“It appears to be in exactly the same good condition, but we advise against eating it,” Chris Albury from Dominic Winter Auctioneers informed the BBC.

Mr Albury expects the listing to get between £300 and £500 ($570-$950)

It also includes an order of service, ceremonial details and a royal wedding breakfast programme.

The auction will take place on August 11.

Image: supplied.

This article first appeared on Over60.