In return for saying yes, the actress received some serious sparkle: an 8-plus carat center stone surrounded by 20 smaller stones. "It's the most beautiful piece I've ever seen," says a close source of the diamond ring. "Arki did a wonderful job."

The pair began dating last summer after attending a private dinner together in Milan. Since then, their relationship quickly heated up despite the fact that the couple lived on different continents (she is based in New York, he in London).

It would be the third marriage for Thurman, who has a son and daughter with ex Ethan Hawke, whom she divorced in 2003. Her marriage to Gary Oldman ended in 1992. Busson has two sons with former supermodel Elle Macpherson, from whom he split in 2005.