The mansion has only had five owners over two centuries (Picture: Google)
A grand ‘giga mansion’ located at 17 Belgrave Square in central London is undergoing a major redevelopment that, once completed, will place it among the capital’s most expensive residential properties.
The Grade I listed building, with origins dating back to 1840, is being transformed by development firm Fenton Whelan. The redevelopment is slated for completion by summer 2026.
Spanning approximately 22,000 square feet, the mansion will incorporate an array of high-end amenities. These include a gym, swimming pool, spa complex, home cinema, orangery, an attached mews house, a three-car garage, and staff living quarters.
The combination of historic grandeur and modern luxury aims to appeal to ultra-high-net-worth individuals looking for a unique London property.
What is a 'giga-mansion'?
The redeveloped mansion will be positioned within London’s ‘giga-prime’ residential market, a category reserved for homes valued over £100 million.
This sub-sector is notably small and exclusive, and it’s thought there are around 20 such properties in the capital, predominantly located in Belgravia, Mayfair, Knightsbridge, and Kensington.
The clientele often comprises billionaires, heads of state, and members of royal families.
Peter Wetherell, executive chairman of Wetherell estate agents, recently told The National that sales at this level occur infrequently, usually off-market, and are ‘cloaked in secrecy and legal non-disclosure agreements.’
Situated just a short walk from Buckingham Palace, the mansion occupies a prime position in Belgravia, bordered by the Austrian Embassy and the Country Land and Business Association.
This central location has long been favoured by royalty, diplomats, and international dignitaries.
Sanjay Sharma, co-founder of Fenton Whelan, told The National: ‘It’s the square for royalty and world leaders and [properties] come to market only very rarely’.
According to Sharma, the prospective buyer is likely to be a billionaire with a cosmopolitan lifestyle.
History of the mansion
Originally constructed in 1840, 17 Belgrave Square has a storied past with just five owners over almost two centuries.
Sir Ralph Howard, a 19th-century Member of Parliament, was among its early inhabitants, hosting figures such as Princess Victoria of Saxe-Coburg-Saalfeld, later the Duchess of Kent and mother to Queen Victoria.
Sir Ralph Howard was the first owner of 17 Belgrave Square (Picture: Hulton Archive/Getty Images)
Queen Victoria’s mother was a guest at the mansion (Picture: Wikipedia)
The property was subsequently owned by politician Pandelli Ralli for around 60 years until his death in 1928.
Later, Lady Leontine Sassoon held the mansion during the mid-20th century, during which it served dual purposes: hosting gatherings for soldiers during World War II and functioning partially as a Red Cross supply depot.
From 1974 to 2013, the building was home to the Royal College of Psychiatrists before it relocated.
In recent years, the mansion belonged to Russian oligarch Georgy Bedzhamov, who has been pictured with Vladimir Putin.
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Fenton Whelan purchased the mansion for £35 million and secured a £29.5 million loan to finance the redevelopment.
The company anticipates selling the finished home for roughly three times that initial purchase price.
Following the completion of redevelopment in mid-2026, 17 Belgrave Square will be introduced to the market as a standout offering within London’s ultra-luxury property sector.
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Its combination of historical significance, prime central location, and state-of-the-art facilities is expected to attract international billionaires seeking prestigious London residences.
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