Cove House, in Sydney's Sutherland shire overlooking the entrance to Port Hacking, was to be auctioned in February unless sold beforehand.

Highland agents Mitchell Wynn and Laura Mckay sold the property to an undisclosed buyer earlier this month.

"This property attracted national and international exposure and attracted a number of genuine and highly qualified buyers with high calibre budgets," the company said.

The sale price was more than $3 million above the shire's previous highest.

The luxuriously appointed house with glass fronted, mosaic-tiled swimming pool and manicured grounds was built across two blocks in Cowra Place in 1973 for sandmining company chief executive Tom Breen.

The design by Sydney-based architect Reuben Lane was inspired by the whitewashed buildings in villages along the Mediterranean coastline.

Similarities were also seen to the Sydney Opera House, which was built at the same time, because of the free form and curved walls.

Mr Breen named the house Apollo Gate from Greek and Roman mythology, but it was renamed Cove House by a subsequent owner.