Word from People.com is the couple got engaged Jan. 9 at a silent-movie theater in Los Angeles.
The pair started dating last spring after Murphy broke up with her "Just Married" co-star Ashton Kutcher.
Jeweler Neil Lane told the entertainment Web site that the ring Kwatinetz presented Murphy was "cool, big, flawless and old."
"A big ol' rock that was flawless, just like Brittany," he added.
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