The pair apparently began dating last summer after attending a private dinner together in Milan, Italy. Busson surprised Thurman with the ring this week in London, where the couple attended the 90th birthday party for Nelson Mandela, according to the Daily News.
It would be the third marriage for the 38-year-old Thurman, who has a son and daughter with ex-husband Ethan Hawke, whom she divorced in 2003. Thurman was previously married to actor Gary Oldman.
Busson has two sons with supermodel Elle Macpherson, from whom he split in 2005.
No wedding date was announced.