"Sex Tape" actress Cameron Diaz was recently spotted sporting a sparkling gold ring on her engagement ring finger, leading witnesses to speculate that her Good Charlotte rocker-boyfriend Benji Madden has popped the question.

Diaz wore the ring during the Hollywood Costume exhibition luncheon in Los Angeles last Wednesday.

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A witness shared that the 42-year old actress was "casually and constantly twirling her ponytail, showing off the ring and often playing with it" during the event. After the said luncheon, Diaz had dinner with Madden at Madeo, an Italian restaurant in Beverly Hills.

A source close to Diaz shared that ever since she began a relationship with the musician, the actress has been "much happier", sharing that Madden has changed the star's life "in a very positive way".

The said insider also shared that the two have been living together for the past few months and despite their busy schedules, make sure that they spend as much time with each other as possible. "During the days, they often share a workout. At night, they often stay at home and cook," the source stated.

Diaz and Madden made their relationship public last May and, according to another source, have openly told their friends and family that they believe that marriage is part of their future.

In an interview with Details magazine, Madden shared that he does think about settling down and starting a family, saying that men do think about the prospect of forever - whether they admit it or not.

Diaz, on the other hand, previously shared that she doesn't believe in monogamy, sharing "Relationships can last two, five or 20 years. I don't believe in sharing your bed with the same person your whole life, though. That might be a reality for some, but it surely isn't for me."

However, it seems that Diaz has had a change of heart, with a source sharing that it wouldn't be a surprise if Diaz called one day and said "Guess what? I'm Mrs. Madden!"

TagsCameron Diaz, engaged, Benji Madden