Singer Britney Spears, right watches the Houston Rockets play the Los Angeles Lakers during the first half of their NBA basketball game, Friday, March 30, 2007 in Los Angeles. [AP]

Justin Timberlake has confirmed reports he reached out to his ex girlfriend Britney Spears after learning she had checked into rehab in February.

The Cry Me A River singer admits his heart went out to the troubled Toxic singer after he heard she'd hit rock bottom after a series of headline-grabbing antics, including shaving off her hair and arriving at Hollywood parties without underwear.

Timberlake says, "I called her because I worried about her.

"She's a great woman. I'm rooting for her. (It) seems like she's getting everything under control now."