Around 40 firefighters worked for hours to douse the blaze on The Bishops Avenue - dubbed Billionaires’ Row - in Hampstead, North London on Monday morning.
While there were no reports of injuries, the roof, first floor and ground floor of the detached property were destroyed by flames.
On Tuesday London Fire Brigade said the fire has been recorded as ‘undetermined’, due to the extensive damage to the building.
Station Commander Rob Hazzard said the property is understood to be unused, as was empty at the time of the fire.
Crews from Finchley, West Hampstead, Hornsey and Kentish Town fire stations arrived at 3.45am and the fire was under control by 6am.
"Firefighters were faced with a significant fire on arrival which involved the whole of this large building,” said Mr Hazzard.
"Crews worked hard to tackle the blaze and bring it under control."
The cause of a large fire at an empty house in #EastFinchley yesterday morning has been recorded as undetermined, due to the level of damage to the building https://t.co/c2HOA5tC6q pic.twitter.com/Gf9jWcbAcc
— London Fire Brigade (@LondonFire) June 7, 2022
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.
Paul McCartney’s ex Heather Mills lived in an apartment in one of the houses.
The Bishops Avenue connects the north side of Hampstead’s Heath to East Finchley.
One eight-bedroom mansion currently for sale on the sought-after street is listed with an asking price of £17m.