Tony DiMaio / Retna Digital 1 / 8
Tony DiMaio / Retna Digital 1 / 8

It's been months since Kate Winslet and Sam Mendes have been photographed together. Still, the announcement this week that they're throwing in the towel after almost seven years of marriage surprised even the most negative matrimonial Nellys.

What did in the big-screen couple, who wed in 2003 and have a 6-year-old son, Joe (the actress is also mom to daughter Mia, 9, from her first marriage to Jim Threapleton)?

According to the tabloids, their careers played a large part in the "entirely amicable" split, which reps say happened earlier this year. But it remains unclear whether the parting of ways was the result of too much or too little together-time (or maybe both).

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Their "work schedules were too intense," a source tells Us magazine. "They just couldn't make it work. They were never together. They are both so work-oriented that they found it hard to find time together."

Not that proximity necessarily helped matters. The British tabs speculate that problems began bubbling up while they were filming the 2008 marriage meltdown drama "Revolutionary Road," on which Mendes, 44, directed Winslet, 34, to a Best Actress Golden Globe.

"Working and living together was incredibly intense and it basically overwhelmed their relationship," a source explains to the London Daily Mirror. "The pair [has] a very different work ethos. Whereas Sam wanted to switch off after a long day, Kate liked to analyze every nuance of her performance. It was just too much."

(Mendes himself confirmed this during an interview with the London Telegraph -- depressingly titled "Hollywood's Golden Couple" -- in January 2009, saying, "I tend to cut off at the end of the day and watch a baseball game or something. I don't like to bring work home. Kate is the opposite. So I just had to change my ways because it's what she needed and my goal was to get the best performance I possibly could out of her and if she needed to talk about it, then that was my job, too.")

Another source backs up the post-film fizzle to the London Daily Mail, maintaining, "Things were extremely rough to say the least recently. Things went downhill after 'Revolutionary Road.'"

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When the Oscar-winning filmmaker later hit the road sans family to shoot "Away We Go," it, "ironically, also proved difficult" for the relationship, says the Mirror's snitch.

"Last year, they both made a commitment to spend the year together and do less work. But it actually ended up with them both going a bit stir crazy," contends the mole. "They are both really driven and were arguing more than ever before."

Winslet supposedly took a job toward the end of 2009 in order to "try and release some of the pressure and tension that had built up between them," the insider continues, but they soon "realized their marriage was on its last legs. They had a series of rows over projects this year and that was the straw which broke the camel's back. They are both devastated but want to stay on good terms for the sake of the kids."

Their supposed squabbling is also noted by another spy, who tells the London Sun they "had been arguing a lot after 'Revolutionary Road,' their last movie together. They were spending a lot less time together. Their closest friends were aware that they had been on the rocks for over a year."

Adds the source, "The relationship was intense and arguments often kicked off. They have been living separately for a while. There had been some huge rows behind closed doors before they decided to formally separate."

And separate they have. The actress, who flew solo while making the red-carpet rounds during awards season, was spotted this week soaking up the sun in Mexico with her tykes, while Sam is reportedly hanging with pals in New England.

"Kate is devastated," an insider concludes to the Mail. "She thought their marriage was forever and now she has two children from two marriages and both are not living with their fathers."

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