Bmw - 535 :: 2009 - Foggy Windshield On A Sunny Day

I got off work at 4:30 pm the other day, and came out to my new (for me) 2009 car, and the front windshield was foggy. No other windows were foggy in my car, and no windows were foggy on any one of the 50 cars in the parking lot, b/c I checked every one as a slowly cruised around the parking lot before I left for home.

I'm 55 yrs old, and have never had a car do this on a sunny, warm day, in late afternoon, with relatively low humidity in the outside air. The windows were rolled up, yet that should not have been the main source of the problem. The windshield was not a little foggy, it was completely fogged up.

It had also been foggy that morning, but so were the other windows, b/c it was a cool, clear morning, and at 7:00 am on a morning like that, it is expected to have some window fog...but not at 4:30 pm after it's been sunny all day, and become warm!

What could cause this?...a windshield that is not sealed properly, or what? I did use the defroster that morning, and it worked fine, btw.