A fossil dating from 200 million years ago was among the hidden secrets uncovered during restoration work at Leeds Castle in Kent.
The nautilus fossil is believed to date from 200 million years ago
The nautilus fossil was found while worn stones were being replaced in the 16th Century Maiden's Tower.
Workmen also found a piece of Kentish ragstone that had been re-used in a previous restoration and may date back to an earlier tower on the site.
The completed work has been described as a once-in-a-lifetime facelift.
Two new exhibitions in the Maiden's Tower are to be opened at the beginning of June by Princess Alexandra.
The first, called The Collection of a Gentleman, will have 24 paintings from the 17th, 18th and 19th centuries by artists such as Gainsborough, Constable, Reynolds and Landseer.
The second will be a mixture of items from the castle's 900-year-old history, many of which have been hidden in attics and storerooms for years.