So much for that amicable break-up, huh?

Just 48 hours ago, Kristin Cavallari and Jay Cutler released a statement that claimed they were getting a divorce...

... but everything was fine and friendly between the stars.

“With great sadness, after 10 years together we have come to a loving conclusion to get a divorce," the former MTV personality and professional quarterback said, adding:

"We have nothing but love and respect for one another and are deeply grateful for the years shared, memories made, and the children we are so proud of.

"This is just the situation of two people growing apart.

"We ask everyone to respect our privacy as we navigate this difficult time within our family."

Sounded unfortunate, yet reasonable at the time.

Cavallari, best known for her role on The Hills, and Cutler were married for about a decade and have three young kids.

Just a day after the bombshell was dropped, though, Cavallari and Cutler's divorce documents were made public -- and they paint a somewhat adversarial  picture.

More than that, Cavallari's official filing makes it sound a lot like Cutler cheated on her.

These official papers allege that Cutler "is guilty of such inappropriate marital conduct as renders further cohabitation unsafe and improper."

Marital misconduct, huh?

What could this mean aside from infidelity?

According to TMZ insiders, Cavallari is actually angry that Cutler filed for divorce before she did -- and that he claimed to be an "at-home parent" who was the "primary caretaker" of their three children in this filing.

So the dispute here and the bitterness here is NOT over another woman.

It's over Cutler's allegation of being a very active and involved father.

(Cavallari is seeking primary custody of the couple's kids, while Cutler is seeking joint custody.)

What does this have to do with "inappropriate marital conduct?" Why did Kristen use such a phrase?

It's a legal thing:

Tennessee is a "fault state," meaning someone asking for a divorce must show fault on the part of the other spouse; hence the accusation of marital misconduct.

It's actually boilerplate language in the state.

The language is included in a divorce petition and counterclaim because Kristin and Jay cannot end the marriage without some showing of misconduct, due to both parties filing divorce documents.

It's then up to their attorneys to determine what, if any, misconduct took place.

This is all a tad bit confusing and, to be frank, not totally important.

The bottom line is that marital misconduct can mean almoost anything in Tennessee legal terms -- from adultery to drug abuse to desertion for a year to impotence to felony conviction.

Despite the assumption of celebrity gossip followers who saw that term initially, it doesn't mean Cavallari suspects Cutler of cheating on her.

This all just means the marriage is over.

And a lengthy legal battle is about to begin.