The How Do You Know star's representative told People.com that her fiancé Jim Toth worked closely with Hollywood jeweller William Goldberg to create the stunning gem.
The ring is Ashoka diamond set on a pave diamond and platinum band.
Reese Witherspoon Engaged
According to William Goldberg, Ashoka stones are extremely rare and less than 10 per cent of raw Ashoka diamonds can be cut like Reese's engagement ring was.
Witherspoon, 34, is just one of a host of celebrities to feel the romance this holiday season.
Natalie Portman, LeAnn Rimes and Lily Allen have all recently announced their engagements.
Reese Witherspoon Engaged
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