The price is understood to be subject to strict confidentiality agreements, but property data website Pricefinder has an $18.75 million notification on the sale. Settlement will confirm that result.

At that level the sale sets a Hawkesbury River record for a residential sale by an extra $10 million, smashing the $7.3 million high for Cattai set a year ago when it was sold by Gendy and Hugh Parry-Okeden, nephew of reclusive heiress and Australia's richest person on last year's Forbes Rich List Blair Parry-Okeden. Known as "Ukamurra", it was sold to a company headed up by a syndicate of Chinese buyers.

The founder of Bras N Things is known for his bullish property deals. After he moved to Singapore in 2013 his two Vaucluse homes, one on Kutti Beach, were sold for a combined $25 million in 2014.

He bought a new residence on Rose Bay's Hermitage Reserve in 2013 for $32 million, with a three-year settlement, and within weeks of taking possession of it he listed it for sale.

Brad Pillinger, of Pillingers, and Deborah Cullen, of Knight Frank, are now asking $47 million for it.

Mr Blundy bought the 57 hectares that make up Sweven in 2001 for $2.05 million, and commissioned architect Timothy Moon to design a dramatic stone and timber residence that took three years to build and an estimated $8 million.

Completed in 2009, it was listed in 2013 and has been shopped around with a handful of agents since then. Neville Rava, of Cutcliffe Property, refused to comment when approached by Domain, but it was being touted among locals as a new record for the area on Wednesday.

Mr Blundy turned to agricultural investment two years ago, paying a reported $100 million for the Paraway's Walhallow and Creswell stations in the Northern Territory, covering 1 million hectares.

He was ranked Australia's 44th richest person in this year's Financial Review Rich List with a worth of $1.39 billion.