Belle Watling is the owner of a brothel that Rhett visits upon occasion. She provides evidence of one of the aspects of Rhett's life away from Scarlett and Tara that infuriates Scarlett at times and makes him all the more attractive, because he's hard to get, at other times. As Scarlett said,
Let me see that handkerchief. R. B. And she's driving away in Rhett Butler's carriage! Oh, if I just wasn't a lady what wouldn't I tell that varmint!
There are rumors that Belle and Rhett have an illegitimate son. Rhett definitely is a friend of Belle's. After the raid on the former slaves who attacked Scarlett, Rhett and Belle cooperate to shield Ashley and other members of the Ku Klux Klan who are at risk of arrest. Afterwards, Melanie attempted to thank Belle.
"How can I thank you enough for what you did for us? How can any of us thank you enough?" Belle: "I got your note saying you was going to call on me and thank me. Why, Miss Wilkes, you must have lost your mind....It wouldn't be fitting at all." Melanie: "It wouldn't be fitting to thank a kind woman who saved my husband's life?" Belle: "Miss Watkins, there ain't never been a lady in town nice to me like you was...And I got to thinking about you being left a widow with a little boy if Mr. Wilkes got hung and he's a nice little boy, your boy is, Miss Wilkes. I got a boy myself..."