The four-AA-red-star, 41-bedroom in Egham, Surrey, was snapped up for an undisclosed sum from the Sutcliffe family, who have owned the Grade-I-listed Tudor mansion since the 1930s.
Set in 50 acres of parkland close to Windsor Great Park, the hotel features the one-Michelin-starred Tudor Room restaurant, which also holds four-AA-rosettes.
Executive head chef Rob Chasteauneuf joined the hotel in March, having previously been group sous chef at Dinner by Heston.
Peter Hinchcliffe, co-owner of Alexander Hotels with his wife Deborah, said: "We're absolutely thrilled to be able to add Great Fosters to our portfolio. It's a wonderful hotel with huge potential, and the fact that we have a Michelin-starred restaurant housed within it adds some significant gloss to our wider offering."
He added: "The hotel has a truly diverse offering, and it's the quality of this offering that first attracted us towards acquiring it. Great Fosters is an excellent and exciting addition to our group and we're looking forward to developing its potential yet further as we marry up our extensive expertise with its outstanding amenities."
Great Fosters has joined what until now has been the four-strong portfolio of Alexander Hotels which includes two hotels in Surrey: the four-red-AA-star, 22-bedroom Langshott Manor in Horley and four-AA-star, 44-bedroom Barnett Hill, near Guildford; as well as the five-AA-star, 58-bedroom Alexander House hotel in Turner's Hill, West Sussex; and the four-AA-star, 38-bedroom Rowhill Grange hotel in Wilmington, Kent.