"She called him on their anniversary and told him she'd be filing for divorce. She wanted to give him fair warning," a source close to the pair told Us.
"Khloe was very firm. She said she will be filing soon, and she thinks it's best they both move on. Khloe told Lamar she hopes he gets the help he needs."
Odom reportedly called his wife daily throughout the course of his downward spiral from his downtown Los Angeles bachelor pad after Kardashian had kicked the NBA basketball free agent out of the $4 million mansion they shared in Tarzana.
"She'd ask if he's cleaned up yet," another source told Us. "And he'd insist he doesn't have a problem."
The couple's prenuptial agreement will reportedly entitle Kardashian to $500,000 for each year they were married, two cars, and a $2 million "bonus" for making it four years together. At the time Kardashian and Odom wed, he had signed a now-expired $33 million deal with the Los Angeles Lakers.
The pair's split will reportedly be a storyline on the upcoming season of E!'s Keeping Up with the Kardashians, which Kardashian and her clan are currently shooting. When Kardashian and Odom's problems hit their peak in September, the former The X Factor host allegedly took a few days off -- away from cameras.
However, "they have to address" the breakup, according to an insider. "It's not something they can avoid."
"They will not drag Lamar through the mud or bash his character," the insider told Us. "He has an illness and deep down is a good person."
A telling sign Kardashian and Odom are headed for a split is on the date of their anniversary, Kardashian tweeted a photo of a gift she had received from her girlfriends -- a rough-cut glass heart that read, "Khloe, Love you 4 ever, Malika & Khadijah" -- rather than something from her husband.