"hot" brakes smell at right rear wheel... ??

[86560SEL]

UPDATE - replaced brake pads on the rear several weeks and all is fine now - no more issues with the brakes. Thanks for all of the replies.

I have not noticed it until today, but when I stopped today to fill my car with gas, I got a whiff of "hot brakes". I smelled and it was coming from the right rear wheel well area (where I was standing). None of the others have the smell. I put my hand down near the wheel and it did not feel hot... warm, but not hot. My brakes work fine and there is no squeaking/scraping, etc, so wondering what could be going on.

(Yes, I checked and the e-brake is not applied).

Thanks for any information.
Btw - the car is a LWB W126 sedan.