In real life they broke up three years ago, but in reel life Cameron Diaz thinks Justin Timberlake still has a lot to learn. Diaz is costarring with her ex in the film “Bad Teacher,” which started shooting in Los Angeles two weeks ago. Diaz plays a jilted 7th grade teacher, usually hung over when she shows up for class, who’s trying to afford breast augmentation on a teacher’s salary; Timberlake is the bespectacled substitute who becomes her romantic prey. The movie will be released some time in 2012.

Diaz and Timberlake dated for four years. The former ‘N Sync singer has since moved on to a relationship with actress Jessica Biel.

The “Charlie’s Angels” star says she’s delighted to be sharing a set with Timberlake. “We’re thrilled to have him,” Diaz told Access Hollywood’s Billy Bush. “He’s the best person for the job. He’s going to be hilarious. He’s clearly a very talented comedian, look at his ‘Saturday Night Live.’ He’s fantastic; he’s going to be so great.”

For her part, Biel is equally sanguine. “I haven’t read the script, but I think it sounds fantastic,” she told E! News. “It sounds like it will be so funny. Obviously, I’m superexcited for him.”