Six fire engines and around 40 firefighters rushed to the house alight on The Bishops Avenue – dubbed Billionaires’ Row – in Hampstead, north London, on Monday morning.
The roof, first floor and ground floor of the detached property were destroyed by the blaze. There were no reports of any injuries.
Station Commander Rob Hazzard, who was at the scene, said: “The property is believed to be disused and empty at the time of the fire, so fortunately there were no reports of any injuries.
“Firefighters were faced with a significant fire on arrival which involved the whole of this large building.
“Crews worked hard to tackle the blaze and bring it under control.”
The Brigade was called at 3.45am and the fire was under control by 6am. Fire crews from Finchley, West Hampstead, Hornsey and Kentish Town fire stations were at the scene.
The cause of the fire is under investigation.
The Bishops Avenue, which has at least 66 mansions, is home to some of the world’s richest people.
The Saudi royal family sold ten properties along the street for £73million, while the Sultan of Brunei is thought to own at least one house there.