A 40-bedroom mansion inside Regent’s Park formerly owned by the Saudi royal family has been sold for about £139m in one of London’s biggest ever property sales.

The Holme, a 2,694 sq metre (29,000 sq ft) residence in 1.6 hectares (4 acres) of gardens, sits next to the park’s boating lake close to London zoo and the US ambassador’s residence, Winfield House. It was put on the market nearly two years ago, with agents reportedly seeking offers as high as £250m.

The mansion has been sold to a UK subsidiary of Zedra, a corporate services firm that advises and manages investments for wealthy people, according to land records, as first reported by the Financial Times. However, the identity of the buyer remains a mystery.

Previously owned by Prince Khaled bin Sultan al-Saud, a member of the Saudi royal family, the property has now reportedly been sold for £138.9m, significantly below sales estimates made when it went on the market in March 2023.

Built in 1818, the Holme had been bought on behalf of Prince Khaled and his family in 1991, but was put up for sale when a loan secured against the property expired.

The sale price would equal the reported £138m agreed for Aberconway House in Mayfair in late 2023 by the Indian billionaire Adar Poonawalla, known as “the vaccine prince” because of his family’s vast factories.

The company which is registered as the new owner of the Holme is controlled by a Zedra entity based in Luxembourg, the FT reported, citing corporate records.

This means the true identity of the residence’s new owner is unknown, despite requirements for offshore companies with UK properties to declare their ultimate owners.

A register of overseas entities was brought in by the previous government to improve transparency about offshore property ownership, although some companies with UK property obscure their beneficial ownership because they are controlled by trusts based offshore.

The Holme – whose name derives from a Saxon word referring to a small island or elevated piece of land in water or a river – is ultimately owned by the crown estate, an ancient portfolio of land and property across England and Wales belonging to the monarch, yet has been made available to buy on a long lease.

The property was called “the ultimate desirable residence” by the BBC when it went on the market for £30m in 1988, when it was described as “possibly the world’s most expensive home”.

Zedra has been contacted for comment.