The 42-year-old actress was first seen with the ring at the Hollywood Costume Luncheon in Los Angeles before also wearing it out for dinner with Benji in the evening.
She didn't appear to be shy about flashing the ring, brushing her hair away from her face and smiling broadly at the cameras.
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they were an item in June after weeks of speculation, stepping out hand in hand in New York City.
Cameron and Benji, the guitarist for pop punk band Good Charlotte, looked happy and relaxed as they headed out together in the city, and weren’t shy about showing their affection for each other. The duo were then spotted on a yacht break together in July.
Despite the duo never verbally confirming their romance, their romantic holidays have spoken louder than words.
If there was still any doubt, Benji's sister-in-law Nicole Richie, put it to rest with recent comments.
Nicole, who wed Good Charlotte singer Joel Madden in 2010, joked that she would take all the credit for Cameron and Benji's new relationship.
"I'm going to take responsibility for everything" Nicole said to Watch What Happens Live. When asked if she approved of their budding romance, Nicole said: "I approve of anything that's going to make Benji happy."