Sienna Miller and Hayden Christensen treat us to some utterly convincing lovemaking in their new movie, "Factory Girl." And it's no wonder: We hear the costars actually coupled on camera.

"It's not simulated," an insider tells us. "They're really doing it."

In the movie, Miller plays doomed Andy Warhol protégé Edie Sedgwick. Christensen plays a folk rocker modeled after Bob Dylan.

It was during the film's Louisiana shoot that Miller ran into another squall in her stormy romance with Jude Law - and turned for comfort to Christensen, the "Star Wars" heartthrob.

"They spent about a month hanging out," says one pal of Christensen. "But then she decided she didn't want a relationship. Hayden was devastated. He really fell for her."

Added a friend of Miller, "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."

Apparently. When it came time to shoot the love scene, word is the former lovers dispensed with the flesh-colored socks and pads favored by actors on less familiar terms. And, once the cameras were rolling, the two 25-year-olds fell into old habits.

At the movie's premiere on Monday, director George Hickenlooper would tell us only: "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."

And was congress actually in session during the shooting?

"I can't comment," Hickenlooper answered. "You'll have to ask Sienna about it."

Miller left the Chelsea Hotel after-party before we could ask about the love scene - and where she now stands with Christensen, who wasn't at the premiere. Yesterday, Miller's publicist said the sex wasn't bona fide: "She's just a really good actress."

But now we're wondering if that "really good actress" forgot a little something Monday night. She'd changed out of the divine white party dress she wore on the red carpet at the premiere into what looked like support hose for the after-party. Even Sid Vicious, who supposedly haunts the Chelsea Hotel's elevator, would've been spooked.

So what's Hayden's excuse?

If he was smart, he'd say "I just banged one of the hottest chicks in the game. Let that be a lesson to all of you who thought I was gay. Fellas, lock up your girlfriends because my lightsaber is coming out!!. Sucka MCs best recognize".

Yawn. Who really cares?

So, just because an actor perform love scenes in a movie with a female co-star, doesn't convince their heterosexuality in real life. Remember, they're actors. You'll be surprised who is secretly gay, or bisexual in the entertainment industry.

Didn't Alec and Kim do the deed on film in The Getaway?

This is just publicity BS to try and get more people to see a movie that not many people are going to see.

I would think you'd be a hell of an actor to get it up to fuck your female co-star during filming when the scene calls for simulated sex.

It don't take much to fool you, does it? Once again, they're actors. Actors, and actresses have professional skills, and abilities to concentrate on other thoughts enabling them to perform erotic scenes.

I suppose this might be a big deal in a world where films like Intimacy, Baise-moi, or Nine Songs didn't exist. But since they do, this isn't really newsworthy.

It's a little different in this case because Sienna Miller and Hayden Christensen are famous actors, unlike the casts of the movies you listed.

And just who are Sienna Miller and Hayden Christensen?

There are well-known actors in Intimacy. There are well-known actors in Nine Songs.

Surprised it took Christensen this long.
I thought he'd always been a wooden actor...

I'll have to assume you're joking. There's nobody in either of those 2 movies that are even a quarter as famous as Sienna and Hayden.

I'm not joking.

OK, I looked up Christensen. Apparently he was Anakin Skywalker. It's surprising he can still get work. Sienna Miller seems to be someone who is well-known for being famous.

You don't know who Anakin Skywalker is? Oooookay.

You also have to look at who performed the sex acts in those movies. Did the so-called well known actors do it?

Then why bother with actual penetration if it is not filmed?

I have no idea who Siena Miller is.

Neither do I. However, I have heard of Sienna Miller.

she's easy on the eyes.

Not everybody's life revolves around what comes out of George Lucas' ass, you know.

this could be interesting. it doesn't change my desire to see the movie though.

Did you miss the point of the thread where the story is that they weren't acting in a love scene but actually had real sex--i.e. real penetration?

So the only people who know who the actor who played Anakin Skywalker is have lives that revolve around Star Wars?

Again I say oooooookay.