Olivia Wilde has Justin Theroux to thank for her stunning engagement ring after he helped her fiance Jason Sudeikis pick out the sparkler.

Jennifer Aniston has revealed her beau played a part in helping Sudeikis choose the diamond and emerald ring as he prepared to pop the question to Wilde.

The Friends star, who became engaged to Theroux last year (12), tells E! News, "Somebody helped him on the ring, in fact... Not me, but my fiance did... He just guided him in the right direction."

Saturday Night Live funnyman Sudeikis, who stars with Aniston in new comedy We're The Millers, announced in January (13) he and Wilde are set to marry after two years of dating.