PHOTO: Simonds Hall in South Yarra. Photo: Jules Tahan

Billionaire property developer and former Toll Holdings boss Paul Little has agreed to buy a historic South Yarra mansion from Christ Church Grammar School for at least $18 million.

The buyers, Mr Little and his investment banker wife, Jane Hansen, plan a major restoration to transform Simonds Hall – a former house-turned-conference centre – back into a residential home after snapping it up in a secret deal before Christmas.

Mr Little lodged a caveat on the property in December, public records show. The price will become public at settlement but is at least $18 million, according to four sources with knowledge of the deal but not authorised to speak publicly.

Although the building is structurally sound, it will offer a multi-year renovation project to its new owners, who previously restored their landmark Toorak residence Coonac and Namarong in Armadale.