Did Ryan Phillippe's supposed need to scratch his seven-year itch doom his marriage to Reese Witherspoon? So claim the tabloids, which have added a new layer of ookiness to the couple's Oct. 30 split announcement by alleging that the easy-on-the-eyes actor may have fallen for a co-star.

According to Us Weekly, Phillippe, 32, has lately "grown close" to Australian actress Abbie Cornish, 24, who appears with him in the forthcoming Iraq war drama "Stop Loss."

Ryan and Abbie purportedly spent quality time together while filming in Austin, Texas, from August through October, cozying up over dinner and hanging out at the actor's pad.

But Cornish adamantly denies anything untoward took place and insists her relationship with Phillippe is strictly professional.

"It's not true," her rep asserts the magazine. "They are co-stars and that is it."

Third party or not, tensions between Reese and Ryan appeared to boil over at the New York premiere of his well-reviewed "Flags of Our Fathers" on Oct. 16.

Multiple outlets are reporting the twosome, who wed in 1999 and have two doppelganger tots, Ava, 7, and Deacon, 3, had a very public spat at the pic's afterparty.

Roger Friedman from Fox News characterized it as a "knock-down, drag-out fight" straight out of "Who's Afraid of Virginia Woolf," while an on-the-scene photographer-blogger named Hughe2030 claims the Oscar winner was overheard telling her husband, "I don't know what you mean by saying I am embarrassing you. How could you say I am embarrassing you?"

As for what led to their ultimate demise, that's still up for debate.

Us says Reese "was alerted" to photos of Phillippe with Cornish and questioned him over whether something was going on.

"Ryan admitted it was true and said, 'We just need to end this,'" a source maintains to the magazine. "Reese literally had no choice."

The National Enquirer, however, believes she found his Blackberry with incriminating messages on it. The tab posits that Phillippe, despite being "caught red-handed," had hoped to salvage the union but Reese opted to stick a fork in it.

TMZ.com, meanwhile, reports the reasons for the bust up were "cumulative" (and no, "cumulative" is not Cornish's nickname) and says the pretty pair decided to part ways several weeks ago.

"She's just tired of all the fighting and bickering," a "close friend of the actress" tells the Chicago Sun-Times, which points the finger at Ryan's "well-known hot temper."

Witherspoon, whose estimated $25 million-plus-a-movie paycheck dwarfs her indie-preferring hubby's $2 million-per-picture, has reportedly sought out the same legal pitbull who handled Jennifer Aniston's divorce from Brad Pitt.

Reese and Ryan, like Brad and Jen, entered married life without a prenup, according to TMZ, which means their mismatched assets would be split down the middle.

To their credit, the estranged spouses are said to be doing their best to keep things civil, although a divorce filing is just "a matter of time."

Rumors of marital woes have dogged the low-key if paparazzi-targeted duo off-and-on for years (the latest round came shortly after Witherspoon's "Walk the Line" Oscar win in February), not surprising given their once refreshing openness about seeking marriage counseling.

"The biggest mistake is not doing that, ignoring it and have the marriage fall apart because of laziness," Phillippe explained to the New York Daily News in 2002, the same year Witherspoon told "Access Hollywood, "I don't think there should be a social stigma attached to having therapy. It's self-improvement."

Still, admitted Reese, "Marriage is difficult and it takes a lot of work. And my husband and I work on it everyday."