Khloe Kardashian -- Brave Face Hides Struggle Over Lamar

Khloe Kardashian is going through hell right now but trying to put on brave face to the world ... or so it seems.

Khloe tweeted a picture of herself Friday night -- looking flawless -- and NOT looking like a woman on the brink. An hour later she offered an explanation, writing "Smile and no one will notice." A pretty clear message.

TMZ broke the story ... Khloe is trying everything she can to save husband Lamar Odom from his downward spiral, which stems from an intense crack addiction.