Brigitte Nielsen in Rehab -- Who Knew?!

In case you thought rehab was just for twentysomethings, TMZ has learned that 44-year-old Brigitte Nielsen checked into rehab a few weeks ago -- and is getting out in the next 24 hours. Clean and sober and completely under the radar!

A source close to Nielsen tells us she checked herself into North Hollywood's Cri-Help treatment facility several weeks ago and is doing well. Although it isn't known what Flava Flav's ex-girlfriend is in treatment for, our source says, "It was her decision," adding "It was the right time." Cheers to that!

Looks like Lindsay and Britney have someone else they can not drink with all night!