Maurice Forsyth-Grant, the former owner of Ecclesgrieg Castle, near St Cyrus, who now lives in a small cottage on the estate, claims he is the target of a sustained campaign of harassment by the current owner, Gavin Farquhar, designed to prevent him from developing his own property.
The property, built by William Forsyth-Grant, and some of the land was required to be sold to pay death duties. Around 400 acres and five houses of the estate were kept by the Forsyth-Grants.
Since the castle last changed hands in 1999 it has been left unoccupied and is falling down with parts of the roof collapsing recently. The Category B listed building has now been designated as a building at risk by the Register for Scotland.
Mr Forsyth-Grant, 50, a descendent of the original owners, said: "We thought by selling it we would get new owners who would have money to invest in it and keep it as a beautiful building. But for the last 15 years since the new owner bought it he has not only trashed the castle and the estate, but has trashed my family."
Aberdeen businessman Mr Farquhar bought the castle and 84 acres of the estate at auction and in May 1999 applied for permission to convert the castle into a 60 bedroom hotel as well as chalets and lodges.
However, after objections to the proposed development by Mr Forsyth-Grant and other neighbours the plans were shelved in 2002.
Mr Forsyth-Grant alleges that Mr Farquhar is trying to force him to leave Ecclesgrieg.
Mr Farquhar is listed as holding eight directorships of different companies including Farquhar Estates Ltd. Despite repeated requests he declined to comment.