Serena Williams' retirement bod is lookin' gooooood ... check out a snap she shared from a recent private jet ride -- she's as trim as ever!
The tennis legend -- who officially hung up her racket in Sept. 2022 -- posted the pic to her Instagram page on Wednesday evening ... and most of her 17 million followers noticed her new, svelte frame.
Many commented on her skinny arms and thin figure ... with one writing, "slim & trim looking great."
Williams then made it clear she isn't using some kind of crash diet to shed the lbs .