The actress, 41, has been spotted spending quality time (and gym time!) with Good Charlotte guitarist Benji Madden, 35, multiple times over the last month.
"They've spent a lot of time at Cameron's house," says one source. "Cameron seems very happy with Benji. He is the nicest guy and treats her like a lady."
The duo worked out together at a Los Angeles Equinox on Friday after hitting the same book launch the night before.
"They seemed very friendly," adds another source of the gym outing. "And they looked like they were trying to avoid [being seen outside], but Cameron was super friendly with other people [at the gym]. She even taught a girl how to use one of the arm weight machines."
Diaz has been friends with Nicole Richie – Madden's twin brother's wife – for quite some time. Perhaps a double date is in order?
Reps for both stars have not responded to requests for comment.