30-year-old Milo Ventimiglia, who stars on Heroes with the 18-year-old cheerleader Hayden Panettiere has a lot to grin about lately. The two have reportedly been sexually involved since Hayden became single, and press for the upcoming season found the duo together in foreign lands.

That trip to Europe publicizing Heroes changed everything for Hayden Panettiere and her costar Milo Ventimiglia. It must have been MIGHTY romantic and we just learned the details about what happened when they came back. (Check out that body language, above.) Hayden and her boyfriend Stephen Colletti (One Tree Hill) went to Les Deux to celebrate her return and things went immediately bad. He must have been suspicious about Milo because he started SCREAMING at Hayden in the club. A witness said the veins in his neck were sticking out. After he finished his tirade he stormed out (for GOOD), but Hayden remained calm. Minutes later Milo strolled in and sat down with Hayden. They partied as if nothing happened and left holding hands.