If you're trying to understand the bizarre behaviour of Britney Spears, take heart. Even someone who dated her for three years is confused -- Justin Timberlake.

In an interview with Oprah Winfrey that aired Wednesday, the talk-show host asked him point-blank: "What do you think is going on with Britney?"

Timberlake, 26, replied: "I don't know, to be honest with you."

Spears and Timberlake first met in the Mickey Mouse Club and later dated until March 2002. It's rumoured Timberlake's bitter break-up song, "Cry Me a River," was written about Spears.

"I haven't spoken to her in years," said Timberlake. "There's no ill will. I have nothing but love for her."

"It's funny because we dated each other at a time," he added. "Wow, I haven't talked about this in a long time, this is interesting."

In the past year, Britney has shaved her head, attacked photographers with an umbrella and given a widely ridiculed performance at the MTV Music Video Awards.

Her new single, "Gimme More," was supposed to signal her grand comeback. Instead, it debuted at Number 85 on the Billboard Hot 100 list, before slowly rising up 10 spots.

Producer Timbaland -- who has enjoyed several hit singles with Timberlake, including "Cry Me a River" -- has said he won't work with Spears again because she's become too "big-headed."

Spears is also currently fighting for control of her two sons -- Sean Preston, 2, and Jayden James, 1 -- in a custody battle with ex-husband Kevin Federline.

A California judge presiding over the case has slammed Spears, 25, for her apparent heavy drinking and drug use.

In court documents obtained by celebrity gossip website TMZ.com Tuesday, Gordon concludes "there is a habitual, frequent, and continuous use of controlled substances and alcohol by (Spears)."

Spears now has to undergo twice-weekly drug and alcohol testing, and talk to a parenting coach who will observe how she interacts with her children.

Lawyer Gloria Allred, who represents a former bodyguard of Spears who gave a written declaration about the pop star's odd behaviour, said the judge didn't go far enough.

"I think, if he thought she really had a substance abuse issue, he should have taken away custody until such time that she could prove she was no longer using alcohol and or substances," Allred told CTV Newsnet.

"I think it also would have given her more incentive to get the help she needs."