The actress met the Brit on the set of the upcoming sci-fi movie last year (10), but they kept their love largely out of the spotlight and refused to confirm the romance.
Agron has now opened up about their relationship, branding Pettyfer "very sweet" and admitting moviemaker D.J. Caruso helped them become a couple.
She tells Britain's Sugar magazine, "The film's director basically set us up. He was like, 'Maybe you should meet this guy before you're forced together in front of the cameras'.
"So Alex and I met for dinner, and I was really worried that it was going to be awkward, so I brought along my dog to break the ice. Within minutes this huge German Shepherd was up in Alex's lap, licking his face. It was so funny!
"Alex might see himself as a bad boy, but he's actually very sweet in real life. And I think it's important to have your differences in any relationship. I wouldn't want to be dating a carbon copy of myself. That would just be boring."