Britney Spears' insecurities about her first true love Justin Timberlake sparked her total breakdown, claims a new book.
Author Steve Dennis alleges in In Britney: Inside The Dream that the singer grew jealous of the effect her then beau Justin had on other women.
The two first met on the set of Disney's The Mickey Mouse Club and began their relationship in their late teens, reports The Daily Star.
One friend quoted in the book said Justin, now 28, "made her so happy". The source added: "He also provided her with the balance she craved. He knew her and she knew him and in Hollywood that ''knowing'' is priceless."
Dennis, who apparently studied the Britney''s topsy-turvy life inch by inch, claims the 27-year-old began suspecting Justin of having an affair with someone else when she saw pictures of him leaving a nightclub with All Saints girls in 2000.
He alleges, Britney confronted Justin, saying: "Why would you leave the club with them? Where were you going?"
And after Justin denied cheating on her, she started becoming jealous of his former girlfriend Veronica Finn.
In the book, Dennis says: "In Britney's defence, these insecurities were born more out of fear of losing something precious than anything else."
Britney herself was stunned at the "accuracy" of the book, according to sources.
An insider said: "This guy has clearly done his homework and the book does tell the real truth about Britney and her life. In her inner circle it's widely accepted her spiral out of control came at the point she started getting jealous over Justin - despite her fears being totally unfounded."