The actress has been married before on screen but never in real-life.
The blonde beauty initially bonded with the former Good Charlotte star because she "has great taste in music," and Cameron told friends that she knew he was "the one" because of his "chivalrous ways," according to Us Weekly.
According to a Monday report from TMZ, trucks have been arriving at Cameron's mansion all morning including catering, The Velvet Garden florist, Classic Party Rentals and Beverage Warehouse.
Although Cameron had already met Good Charlotte rocker Benji years before, it was her good friend Nicole Richie - who is married to Benji's twin brother Joel - who set them up together.
Benji, who now performs in a group with Joel under the name The Madden Brothers, has also formed a close bond with Cameron's mother, Billie.
An insider for Us Weekly previously said: "Billie absolutely loved Benji. She has been gushing about the relationship, saying she hopes Cameron settles down with him."
The Other Woman star recently admitted "timing" was the secret to her happy relationship.
Cameron Diaz previously dated chart topper Justin Timberlake, who later starred opposite her in Bad Teacher
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She said: "You have to find someone in the same place as you are. Timing is everything. If you get into a relationship where you want something the guy doesn't want, it's never going to work. You're never going to get him to be in that place. No matter how old you are, finding the guy who's in the same place as you are and wants to show up is the only way a relationship works, period."
The news of possible wedding bells may come as a surprise as four years ago, she hit out against marriage for life.
She told Stylist magazine in July 2010: "I think the big misconception in our society is that we're supposed to meet the one when we're 18 and we're supposed to get married to them and love them for the rest of our lives. Bulls**t."
She added: "Who would want to be with the same person for 80 years? Why not break it up a little bit."
Cameron also added in some personal advice as she said: "Have someone for five years and another person for another five years... Life is long and lucky and yes, love might last forever, but you don't always live with the person you love forever."
- Daily Mail