Kevin Federline began tearing up the furniture and punching walls with his fists. Fearing that she would be next, the singer grabbed her sons Sean Preston, one, and two-month-old Jayden James, and bolted to the Four Seasons Hotel for safety writes NW Magazine..

"Kevin has always been hot-headed and he likes to bang things around," notes an insider. "Britney learnt to deal with him kicking the walls now and then.

"But lately, that sort of behavior has escalated to frightening new levels - and recently it hit crisis point."

In her petition, Britney Spears asks for both legal and physical custody of the couple's two children, one-year old Sean Preston and two-month old Jayden James, with Federline getting reasonable visitation rights reports TMZ.

As for money, sources tell TMZ the couple, who married in Sept. 2004, has an iron-clad prenup. Spears is waiving her right to spousal support. She's also asking the judge to make each party pay their own attorney's fees.

Spears gives the date of separation as yesterday, the same day she made a surprise appearance on David Letterman to promote Will Ferrell's new movie. Britney Spears showed off a blunt blonde bob , and her svelte body.

"Oh, my god," David Letterman exclaimed, standing up to shake her hand and plant a kiss behind her ear People reports. "Hi, how are you? Nice to see you. Oh, you look wonderful."

"Thank you so much," she said. "I'm in town, and I'm just such a huge fan. I had to stop by."

"That's very nice of you to say," said Letterman. "That means so much to me."

Said Spears: "Uh, no, I wasn't talking about you. I was talking about Will Ferrell."

According to US magazine, Britney's new body is all natural, Britney went on a strict diet and dance regime to shift her baby weight after delivering Jayden by Caesarean section on September 12.

Spears has hired powerhouse celebrity divorce lawyer Laura Wasser, who has repped a number of celebs, including Angelina Jolie, Nick Lachey and Kiefer Sutherland. We're told Reese Witherspoon and Ryan Phillippe asked Wasser to rep both of them in their split, but Wasser declined for personal reasons.