Kevin Federline was preparing to divorce Britney Spears

Britney Spears' sudden filing for divorce from Kevin Federline on Nov. 7 after two years of marriage was a big shock to Kevin, Life & Style reports.

"Kevin is focused on his tour," says an insider. "I don't think he was prepared for this."

Insiders say Kevin was preparing a divorce bombshell of his own.

As early as last May, Kevin, 28, began secretly meeting with his lawyer, Mark Kaplan, to work out a settlement deal with Britney, 24. Kevin was prepared to use their son, Sean Preston, now 1, as leverage: If Britney didn’t give Kevin $10 million, plus their $10 million Malibu mansion, he would sue her for custody, claims an insider. “Kevin knows that Sean is Britney’s Achilles’ heel,� an insider says.

But the couple stayed together through the birth of their second son, Jayden James, now 2 months. Yet Life & Style knows that Kevin recently went back to his lawyer for more secret divorce talks - and this time, he had two babies to use as pawns. He was hoping to score a $30 million payday.

"He feels like $10 million is not a generous amount if he and Britney split since he won't have any part of his sons' lives," says an insider.

"There was no way she was going to let Kevin lead the way on this subject," says a close friend of Kevin's. "She filed first to save face. It's all about taking care of the babies and keeping the money."

According to the prenup, Kevin will receive $300,000, any gifts Britney bought him that cost less than $10,000 and half the value of their $10 million Malibu mansion.

After a bitter fight on Oct. 11, Britney told him, "If you want to act like you're a bachelor who doesn't have a family or a wife, I can make that a reality," says a friend who witnessed the fight. Brit later got on the phone with her mother and told her, "This isn't working."

That was obvious during Kevin and Britney's recent trip to NYC. She arrived on Nov. 2, the day after Kevin, who was in town to promote his debut album, Playing With Fire. But Britney did not go to Kevin's album-release party at Stereo on Nov. 3 or his poorly attended concert at Webster Hall on Nov. 4.

They even stayed at separate hotels. In fact, the only public appearances Britney made were on Nov. 2 for dinner at the Regency Hotel, which she left in tears after Kevin stood her up, and a surprise visit to the Nov. 6 Late Show With David Letterman, where she showed off her svelte post-baby body - and her wedding-ringless hand.

"I have two young kids now," Britney told a Planet Blue employee while shopping at the Malibu boutique on Oct. 22. "I have to think of them. To be honest, I don't care if we stay together. I'm not going to stop my life for him, and I've already wasted too much time already."

In other news, Dennis Alexander, the father of Britney's first husband Jason Alexander, tells PEOPLE he's "not at all surprised" that Spears filed for divorce. "Not a shock. Does anything last in Hollywood?" he says to People.

"She would totally have had a better chance at it working out if she'd have stayed with Jason."