A monumental transformation is underway in the heart of Belgravia, where a historic Grade I listed building is being converted into a £110 million 'giga-mansion', positioning it to become one of the most expensive residential properties in London.
A New Benchmark for London Luxury
The development firm Fenton Whelan is spearheading the ambitious redevelopment of 17 Belgrave Square, a property with origins dating back to 1840. The project, scheduled for completion by summer 2026, represents a significant investment in London's ultra-prime property market.
Spanning an impressive 22,000 square feet, the mansion will feature an extensive suite of high-end amenities designed to cater to the most discerning buyers. The property will include:
- A state-of-the-art gym and swimming pool
- A comprehensive spa complex
- A private home cinema
- An elegant orangery
- An attached mews house
- A three-car garage
- Staff living quarters
Understanding the 'Giga-Prime' Market
This redevelopment places the property firmly within London's exclusive 'giga-prime' residential market, a category reserved for homes valued at over £100 million. This rarefied sub-sector comprises only around 20 properties across the capital, predominantly located in prestigious areas like Belgravia, Mayfair, Knightsbridge, and Kensington.
Peter Wetherell, executive chairman of Wetherell estate agents, recently explained to The National that transactions at this level occur infrequently and are typically conducted off-market, often 'cloaked in secrecy and legal non-disclosure agreements'. The clientele for such properties typically includes billionaires, heads of state, and members of royal families.
A Property Steeped in History
The mansion at 17 Belgrave Square boasts a remarkable history with just five owners over its nearly two-century existence. Originally constructed in 1840, its early inhabitants included Sir Ralph Howard, a 19th-century Member of Parliament who hosted notable figures such as Princess Victoria of Saxe-Coburg-Saalfeld, later the Duchess of Kent and mother to Queen Victoria.
The property was subsequently owned by politician Pandelli Ralli for approximately 60 years until his death in 1928. During the mid-20th century, Lady Leontine Sassoon owned the mansion, where it served dual purposes during World War II by hosting gatherings for soldiers and functioning partially as a Red Cross supply depot.
From 1974 to 2013, the building housed the Royal College of Psychiatrists before it relocated. More recently, the mansion belonged to Russian oligarch Georgy Bedzhamov, who has been photographed with Vladimir Putin.
Fenton Whelan purchased the mansion for £35 million and secured a £29.5 million loan to finance the comprehensive redevelopment. The company anticipates selling the completed property for approximately three times the initial purchase price.
Prime Location for Elite Residents
The property's location is undoubtedly one of its most significant assets. Situated just a short walk from Buckingham Palace and bordered by the Austrian Embassy and the Country Land and Business Association, it occupies a prime position in an area long 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.
Following its completion in mid-2026, 17 Belgrave Square will enter the market as a standout offering in London's ultra-luxury property sector. Its unique combination of historical significance, prime central location, and state-of-the-art facilities is expected to attract international billionaires seeking prestigious London residences that offer both heritage and modern luxury.
