QT's leading star for "Once Upon a Time in Hollywood" was on set Monday in L.A. getting ready to shoot a scene, decked out in a black turtleneck, white skirt and matching go-go boots.
We don't have to tell you how much she looks like Sharon, we'll just show you. Here's a photo of Sharon with her husband, Roman Polanski, in 1968 ... a year before she and 4 others were brutally murdered by the Manson family.
Sharon was 8 1/2 months pregnant at the time she was killed in '69. Margot's already shot scenes with her faux pregnancy belly.
If her acting is anywhere near as spot-on as her look is -- and Sharon's sister indicated to us earlier this year that it is -- then we're almost certainly in for some Oscar-worthy work.