The sale result is almost double the $10.75 million that retired car dealer Ray Harris and his interior designer wife Robyn paid for the 1870-era residence in 2009.

Sources say a couple approached the Harris family to buy their historic residence with a local agent rumoured to be involved in the negotiations.

The property was designed by renowned colonial architect Thomas Rowe and had been extensively renovated during the Harris family's eight years ownership.

Ashton stood on 2100 square metres a decade ago when it sold as a mortgagee sale for $12.2 million to property developer Southern Cross Group. A subdivision followed, with the front parcel now apartments, and the rear 1070-square-metre block on which Ashton House sits sold to the Harris family.

The sale result tops the neighbourhood's top non-waterfront house sale of $15 million paid in 2009 by car dealer and racehorse owner Terry Mullens for the mariner villa Jenner House. In 2014 Mullens listed Jenner House for sale with a $20 million asking price but it never sold.

Exclusive Billyard Avenue with its prime north-facing, waterfront residences have long commanded the suburb's highest sales results. Boomerang, the waterfront residence had set a high in 2002 at $20.7 million before it sold to transport magnate Lindsay Fox in 2005 also for $20.7 million.

The suburb high is held by the residence two doors away at $23.5 million set a decade ago when it was bought by businessman Theo Onisforou.