Yesterday (Thursday), estate agent Rager and Roberts confirmed contracts had been exchanged on the listed building.
The property was put on the market in May 2007 with a guide price of £850,000 but the cost of the landmark plummeted to £595,000 in January.
Rob Wassell, a Surrey man who set up the Belle Tout Preservation Trust and planned to open the landmark to the public, says he is closing down the not-for-profit trust.
Mr Wassell said, "The trust intends to wind up the company and its operation although it will keep the website updated in respect for this magnificent building and as an information resource relating to its history.
"I would personally like to thank everyone who has supported us on this exciting adventure."
