The pair were spotted in fits of uncontrollable laughter on the set of their new joint project, Bad Teacher.
There's clearly not a trace of bad blood between the twosome following their break up in 2007.
They're obviously having a ball filming the new romantic comedy. In it they both play high school teachers - Cameron's character gets dumped by her rich older boyfriend and decides to try and seduce a substitute teacher, played by Justin.
Cameron, 37, and 29-year-old Justin dated for four years before their amicable split. And if these pictures of them are anything to go by, they've remained good friends.
Celeb fans hoping they might rekindle their romance will be disappointed though – Justin is currently dating actress Jessica Biel.