Aprirose has acquired the De Vere Theobalds Estate hotel for £24.2m from De Vere Hotels, owned by Starwood Capital.
The American private investment firm is looking to sell off its De Vere properties following its sale of its Principal portfolio to French investor Covivio earlier this year.
The Grade II-listed, 140-bedroom property in Cheshunt, Hertfordshire was built in 1763 before becoming a hotel in the 1990s.
Manish Gudka, chief executive of Aprirose, said: "Our hotel business continues to go from strength to strength. We're continually looking for assets that we believe will flourish in our portfolio. Under the leadership of our hotel team we are developing market leading hotels in this thriving sector."
The real estate investment company also owns the 26-strong QHotels portfolio of hotels, which it acquired for £525m last year, and the 275-bedroom Mercure Bristol Holland House Hotel & Spa.