Robin Wright Penn has filed for divorce from her husband Sean Penn, PEOPLE has learned. The papers, filed in Marin County, Calif., on Aug. 12, state that “both parties have already agreed to [shared] custody” over their minor son, Hopper Jack, 16, and that “the estranged couple have already agreed to division of all property.”

That’s a shame. Let’s send them a sympathy card. Or a Crate and Barrel egg separator from their “getting back together” registry. Christ on a crutch. We don’t even know any more.

Robin spent the week walking red carpets, flirting with Quentin Tarantino, chatting up Brad Pitt, and, our source said, "partying every night — but particularly enjoying herself at the Art of Elysium/Cartier party at Soho House, clearly having the best time without Sean. He's just jealous."

So basically this is how it goes in Sean's head: "God, my wife is boring. I need to be with someone young and exciting. I know! I'll screw Natalie Portman! That'll be loads of fun." So he files for divorce, commences with the Portman porking, then sees Robin all sexed up and having fun without him and says, "Hey, look, she can have fun. Maybe I'll call off that whole divorce thing and we'll have fun together. That sounds much easier than getting a divorce." Except that Sean didn't think about the possibility that maybe Robin's having fun because she's not with him.

Just weeks after Star first broke the news that Sean Penn was caught making out with Natalie Portman at L.A.ís Sunset Tower Hotel, the Oscar winner filed for separation from his wife of 13 years, Robin Wright Penn. Now Star has learned that Sean, 48, and Natalie are still seeing each other!

ìShe stimulates him in ways no other person has, mentally or professionally,î says a source. ìThereís a lot more there with Natalie than any of the other girls Seanís been with.î

It was Seanís mid-March indiscretion with Natalie that encouraged Robin, 43, to stop turning a blind eye to her husbandís philandering. ìShe was furious he was messing around with such a young star,î says an insider. ìIt made her sickly jealous.î

And with that, she told Sean sheíd had enough and expected him to be a faithful husband and father. ìShe told him how it was going to be,î says the source. ìBut Sean did it his way and filed. He can be a real jerk like that. This will not be a smooth divorce.î

[During] Deanís acceptance speech for his Best Actor win for Milk, he failed to mention his long-suffering wife, who sat just a few feet away, crying. It was in the weeks that followed the award ceremony that Sean first met up with Natalie. Will Sean be faithful to Natalie? Not likely, says the source. ìHeíll still hook up with girls. Itís what Sean always does.î

When we think of Natalie Portman, we picture her studying Sanskrit or giving immunizations to third world children; we don't usually think wanton maneater with a taste for Spicolis. That's Lohan's job.

Back in 2007, Sean Penn filed for divorce from wife Robin Wright Penn, then they decided to give it another go, but it seems that it hasn't worked out, as Sean just filed for legal separation, "Extra" has exclusively learned.

The two have been married since 1996 and have two teenage children. It's been a big year for Penn, 48, who won nearly every major award for his work in "Milk," including a Best Actor Oscar.

Last time they filed, the couple sought joint custody of the kids, which will likely be the case again this time. Penn was previously married to Madonna.

We really hope this sticks this time. First of all, there's not really any excuse for a man not thanking his wife in his Oscar acceptance speech. Second of all, Sean Penn should be off inflicting his dirty-old-man mustache on young starlets. That's just his nature. There's a reason we always accidentally type "Sean Peen". And Robin, she should easily snag a younger, prettier man, one with a malleable ego who can be trained to treat her as an unparalleled goddess. It just seems natural.

Sean Penn continues to live up to his reputation as a womanizer.

In the April 6 issue of Star, on sale today, we report that the married actor ó who had his wife Robin Wright Penn on his arm at the Academy Awards ó was seen in a passionate embrace with Natalie Portman.

Following dinner at Sunset Tower Hotel's Tower Bar on March 17 ó during which they were "constantly touching each other" ó Sean, 48, and Natalie, 27, hooked up. (They previously served together on the jury at the Cannes Film Festival in 2008.)

"They went to a bank of elevators that only goes to the spa or to private rooms," an eyewitness tells Star. "They came back about 45 minutes later, and that's when I saw them making out."

"There's a door outside of the hotel's Tower Bar that has a bridge to the terrace, so it's semi-private," the eyewitness explains. "I used that path to get to the restroom, and when I came back, I had to go through some curtains ó and that's when I interrupted Sean and Natalie! When they saw me, they were startled and quickly composed themselves."

Whatever. They weren't making out. They were reading to each other from one of Neitszhe's original manuscripts (bought at auction at Sothby's and encased in protective plastic sheeting) and then talked about their "technique". (Acting, not screwing.)

P.S. We're sick of Sean Penn supposedly hooking up with all of these starlets. Just once we want to read about Robin Wright Penn spending a night on the town carousing with hot young dudes, making out with Robert Pattinson in a banquette. She deserves it.

Sean Pennís ìMilkî costar James Franco has further dished about the pairís lengthy on-screen kiss. Franco told Out magazine, ìAfter our [on-screen] kiss, Sean texted Madonna – his ex-wife, Madonna – and said, ëI just popped my cherry kissing a guy. I thought of you. I donít know why.'"

Aw, that's sweet. Not as sweet as "I just got a train ran on me by 6 leather daddies and thought of you", and not nearly as touching as "anal fisting: accomplished! Thinking of you", but still, the sentiment is there.

When I read the script, there was like, one kissing scene. No problem. It's acting….So, but as soon as I signed on I get a new script. Page five, like, full-on love scene. There's like three to five new love scenes in the movie. Gus! What's goin' on? And he said, well, Sean wants it. Sean asked for the love scene.

Sean's doin it. If he wants to do it, who am I to say no? So the first day of shooting I had to do this scene where everybody else is in clothes and I have to dive into the pool naked. And I was very uncomfortable but the make-up artist on the day handed me this prosthetic penis and said here, you can wear this. It'll make you more comfortable…The scene went on for a long time, like half the day. It's just getting old ó diving into this pool naked. And I go over to Sean and I guess he didn't know I was wearing a prosthetic. And I said to Sean, 'You are such a great actor. You wouldn't do a scene like this if they asked . You wouldn't dive into the pool naked,' and he said, not knowing I was wearing a prosthetic he said, 'Well James, if I was built like you, I would.' I didn't say anything. Cut to a couple weeks later we did this scene. We're both dancing and we're both naked, and we both now had prosthetic penises. He finally put it together that I'm wearing the Boogie Nights prosthetic. And he said 'James that time in the pool!' And I said 'Yeah I was wearing the prosthetic.' And he said 'God, I'm so relieved.' And then, he's like 'You show me your prosthetic, I'll show you mine.'

We're kind of surprised that Penn wasn't able to spot the stand-in schlong immediately. We would have thought that he would have ample rubber ramrod experience after being married to Madonna.

There's never a simple reason for a couple to part after 20 years. But if Sienna Miller didn't cause Sean Penn and Robin Wright Penn to split up, some claim she may not have been a good influence.

A source recalls a party in a suite at a New York hotel where they both were staying.

"Sienna was sitting on Sean's lap," according the source. "She was dressed very sexily. She had her arm around his neck." That night, claims the source, they stayed up quite late.

One Penn friend maintains there was never anything romantic between them. "Sienna is like that with everyone," says the friend. "She's very physical. She drapes herself over people she likes. She doesn't mean a lot by it."

Miller's rep insists that suggestions that the actress, now dating Rhys Ifans, was ever more than friends with Penn are "outrageously untrue. Sienna is a very good friend of Robin. She adores and respects Robin."

Still, you wonder if the up-till-dawn scene might trouble a wife left home with two kids.

We're sure that when confronted by Robin, Sienna defended herself thusly: "What's the big deal, old lady? Not everyone likes to stay home and knit while watching PBS. Some of us like to party. And by party I mean rub my cooter all over your husband's leg and run my tongue down the side of his face while he watches strippers who are not nearly as hot as me. It's the friendly thing to do, and I'm a friendly girl."

Though Sean Penn and soon-to-be ex-wife Robin Wright remain tight-lipped about the events leading to their breakup, Star Magazine reveals the sordid details of their last weekend together.

It all started innocently enough, according to the magazine, with an intended romantic getaway in Lake Tahoe, Calif. The couple checked in to the Squaw Valley resort just days before Christmas, but sources said Sean didnít request couple-friendly accommodations.

ìSean didnít spend much time with his wife ó he booked her a separate suite ó and when Robin got fed up with being alone, she went over to his suite,î an insider revealed. There, she ìfound him drunk with two Russian girls!î

Allegedly the actor continued to party the night away, while Robin was nowhere to be seen. ìWhen asked where his wife was, he answered, ëWho cares?íî

You know who cares, Sean? The American people. The American people care. Think of all those Katrina victims who will lose their faith in love because of your reckless disregard for the bonds of matrimony. They've been through so much already, they don't need that. Brad Pitt would never do that to them.

ï Mischa Barton got arrested for DUI and drug possession. Way to be Scrooges, cops. (TMZ)

ï Fergie is engaged! To a man, even! Flossy, flossy. (A Socialite's Life)

ï Jessica Alba is also engaged. Awwww, now her baby won't be a bastard. Cute! (Derek Hail)

ï Robin Wright and Sean Penn are not engaged, however. In fact, they are getting a divorce. Perhaps she finally got a glimpse of him in the cold hard light of day. (I Don't Like You In That Way)

ï Et tu, Brendan Fraser and wife? Oh, Encino Man, why can't you and your onion field hair plugs make love last? (Celebitchy)

ï The sirer of Jamie Lynn Spears's unborn doohicky might not be Casey Aldridge. It might, instead, be Kevin Federline. Juuuuuust kidding, it's some old dude. (Yeeeah!)

ï Gaze upon these photos of Nicollette Sheridan in a bikini and be revived. And then note sadly that Michael Bolton is the master of that body, and shrivel, groaning in pain. (Drunken Stepfather)

ï Sharon Stone trots out those nips for a trip around the block. (Celeb Warship)

ï Lindsay Lohan might as well face it, she's addicted to dong. (Egotastic!)

ï Leelee Sobieski. TeeTee Boobichesti. (The Blemish)