The luxury country house hotel was granted planning permission for refurbishment in 2009, and was expected to open in time for the 2012 Olympics.
Owned by real-estate tycoon and billionaire Gerald Chan, the 46-bedroom hotel has confirmed on its website its first official opening date.
Bookings will open on 8 May.
The six-year delay in opening is said to come as a result of continual changes to the original plans.
It has been confirmed in the Financial Times that Skye Gyngell has remained with the project as chef director since its inception, a role she took on after leaving Petersham Nurseries. Chan also owns Gyngell’s Somerset House restaurant, Spring.
In the six years of development, a revolving door of chefs and managers have come and gone, including executive chefs Chris Staines and Barnaby Jones; and general managers Charles Oak from the Mayfair Hotel, and Henry Gray, who now manages Six Senses in Bangkok.
Ben Thompson is overseeing the hotel’s interior design, and was recruited to the project three years ago to “rescue the hotel”.
Design is expected to create the atmosphere of staying at a “relative’s country house”.