A New York Daily News insider reports that Sienna Miller and her co-star Hayden Christensen were actually having sex during the film’s signature steamy love scene.

“It’s not simulated,” an insider tells us. “They’re really doing it.”

In Factory Girl, Si Si plays Andy Warhol protégé Edie Sedgwick and H.C plays a folk rocker patterned after legendary musician Bob Dylan.

“They spent about a month hanging out,” says one of Hayden’s buddies. “But then she decided she didn’t want a relationship. Hayden was devastated. He really fell for her.”

“Sienna wanted to try to make another go of it with Jude. But, again, it didn’t work out. At the end of last summer, she and Hayden ended up in Toronto for more shooting. They hadn’t talked in six months. But it turned out to be a great reunion,” a Si snitch dishes.

The insiders claim that once in bed together onset, S&H had no problems falling back into old habits.

“Sienna and Hayden grew close during the filming. It was an emotional experience for all of us.” As for the sex, he said, “We tried to portray it tastefully,” says the film’s director George Hickenlopper.

As for whether or not the pair were actually mating on camera, George says, “I can’t comment,” Hickenlooper answered. “You’ll have to ask Sienna about it.”