Kevin Federline's Explosive Tell-All Memoir Sent Britney Spears on 'Downhill' Spiral That Led to DUI Arrest: 'It Really Impacted Her'

Britney Spears has not been doing well since the release of ex-husband Kevin Federline's bombshell memoir last fall.

"It was the Kevin book that really sent her over the edge, and it’s been downhill from there," a source close to the former pop star told an outlet following her DUI arrest on Wednesday, March 4. "It really impacted her emotionally."

"The truth is, this has been going on for a while," the insider added. "Her behavior has become increasingly erratic in recent months. She goes from being fine to being not."

The source also shared that the "Toxic" singer, 44, "feels like she gave Kevin everything that he wanted over the years" and "paid him so much money," only to be "exploited" by his tell-all book.

"He used her; he wanted to ruin her," they said. "And that was a really hard pill to swallow; it absolutely killed her that someone would want to damage her so much."

Federline, 47, spilled some shocking revelations in You Thought You Knew, including that the mom-of-two allegedly paid more attention to their younger son, Jayden Jaymes, while neglecting Sean Preston Federline.

"I don't doubt she loved them both, but her actions made it clear who came first," he wrote. "Preston carried that pain for years. The night terrors, the need for constant reassurance, the feeling that he wasn't loved as much as his brother — it lingered. Even as he got older and could articulate his feelings, the scars remained."

The former dancer, who was married to Britney from 2004 to 2007, further alleged that their eldest child, 20, told him Britney once "punched [him] in the face."

Kevin also claimed the "…Baby One More Time" hitmaker fed Jayden, 19, shellfish and took him horseback riding despite his severe allergies to the food and horses.

"One night, after another unsettling visit, the boys came home and said, 'We're done. We're not going back,'" he added. "You could feel the tension in our house evaporate. They weren't bouncing between two worlds anymore."

The DJ admitted Britney's erratic behavior makes him fear she will eventually meet a similar fate as Michael Jackson or Amy Winehouse.

"The truth is, this situation with Britney feels like it's racing toward something irreversible… From where I sit, the clock is ticking, and we're getting close to the eleventh hour," he penned.

Britney was taken into custody in Ventura County, Calif., after her BMW was seen swerving in and out of traffic on Wednesday.

Per TMZ, the "Oops! … I Did It Again" singer was pulled over by California Highway Patrol just before 9:30 p.m. and booked at around 3:02 a.m. on Thursday.

She was subsequently taken to the hospital "immediately" after to have her blood alcohol content determined. It's since been reported that an unknown substance was also found in her car.