Contents of Greystoke Castle, near Penrith, are set to go under the hammer today.
Lots include a rare portrait by 18th century artist Romney and other items of historical interest.
The sale will be conducted by Cockermouth-based firm Mitchells, which said it was unable to comment on why the castle contents were being sold.
On offer are some 500 lots, including the oil painting by Romney, the most fashionable portrait artist of his day, who was born at Dalton-in-Furness.
It depicts Charles Howard of Greystoke, 11th Duke of Norfolk, and is signed and dated 1777.
Measuring 77cm by 65cm framed, the portrait has a label indicating that it featured in the Abbot Hall Cumbrian Characters exhibition in 1968. It is expected to sell for £15,000 to £20,000.
Another lot of historical interest is an 18th century oil painting of Bonnie Prince Charlie, possibly by James Worsdale.
The portrait is rumoured to have been a gift from the Young Pretender himself, who hoped to bribe his way through the northern chain of castles on his way south with his Scottish army in 1745.
It is well documented that the Prince was right- handed, yet in this picture his sword scabbard is hanging on his right side, making it nearly impossible for him to have drawn it properly — an error which has never been convincingly explained. The portrait is valued at between £3,000 and £4,000.
An oil painting on canvas Greystoke Castle Cumberland about 1800 after its enlargement by Charles Howard 11th Duke of Norfolk” in the manner of Jacob Thompson, of Penrith, has an estimate of £1,500-£2,000.
Furnishings from the castle include a pair of mid-18th century Rococo carved wood pier glasses with an estimated price of £15,000 to £20,000.
These two large mirrors measuring 10ft in height formed the main part of the remnants of the contents following the occupation of the castle during the Second World War by Polish prisoners of war.
