Cliveden, the country house hotel in Berkshire famous as the setting for the Profumo scandal of the 1960s, has been sold to Von Essen Hotels, along with the Royal Crescent hotel in Bath.
"The deal was completed at 11pm last night and we have taken control of both hotels this morning," said operations director Nicholas Romano.
The sale price has not been disclosed, but owner Lazard, the investment bank, had been asking £50m for the two properties and Romano said Von Essen had faced "very fierce competition" to buy the hotels.
Cliveden has 35 bedrooms, while the Royal Crescent has 42.
All 350 hotel staff will be retained by Von Essen, including Cliveden's Michelin-starred chef Mark Dodson.
Cliveden's general manager, Laurence Beere, will not transfer automatically, as he is part of the group's corporate team. But "discussions are in place", said Romano.
Romano added: "Cliveden and the Royal Crescent very much fit in with our portfolio and with what we are continuing to acquire. Cliveden is the finest country house hotel in Great Britain."
Privately-owned Von Essen, which has six hotels, including Ston Easton Park near Bath and Thornbury Castle near Bristol, plans to spend about £5m at Cliveden over two years, modernising the conference facilities and adding a "state-of-the-art" spa.
It is likely to spend about £500,000 sprucing up the Royal Crescent, which recently added a new spa.
The purchase does not include Cliveden's 35-bedroom Townhouse hotel in London, which has been retained by Lazards. But Romano said: "We are considering it."
And he added: "We're in the process of some major acquisitions in Scotland."