When Britney shows her flat belly...you know she is feeling better.

Miss Spears is gracing the cover of December's Rolling Stone looking much like her old self again. Brit tells the mag that her son has been running around dropping the F-bomb. She says, "Preston says the f-word now sometimes. He doesn't get it from us. He must get it from his daddy. I say it, but not around my kids."

Oh, that was a low blow at K-Fed. The pop princess and ex hubby Kevin Federline have two sons together. He better watch his mouth!