Katara Hospitality Co purchased its share of the hotel, formally known as Fairmont Hotel the Savoy, from Lloyds Banking Group, Kingdom Holding Co said.
KHC, 95 percent owned by Saudi billionaire Prince Alwaleed bin Talal, owns the other 50 percent of the Savoy.
The transaction "further solidifies the strategic partnership" between Alwaleed and the Qatari government through KHC, the Saudi firm said.
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KHC owns 35 percent of Fairmont Raffles Holdings International Hotels Co in partnership with the Qatar Investment Authority.
The Savoy, built in 1889, was London's first luxury hotel and became home to Hollywood stars including Charlie Chaplin and Frank Sinatra.
It was also where Queen Elizabeth II, then a young princess, was first seen in public with her future husband, Philip.
Then-prime minister Winston Churchill held meetings at the hotel's Savoy Grill during World War II.
Alwaleed's diversified KHC also has investments in other luxury hotels including The Plaza, New York, and George V in Paris.