Britney Spears’ manic behaviour can be pinpointed to the moment when she first started seeing Kevin Federline.

That is the opinion of one professional who explained his thoughts to E!’s True Hollywood Story of the pop wreck’s life.

Dr. Drew Pinsky believes that since she began dating K-Fed, whose fiancé at the time Shar Jackson was pregnant with his second child, Britney Spears slowly descended into the state she is in today.

He says: "If you take Britney's life and put a moment in time where things started getting bad, it's the moment she got involved with Kevin Federline.

"That's when things started to unravel," he adds.

Take a sneak peak at the documentary, and other people’s opinions on the Britney circus here.