Christie Brinkley redefines “scarlet woman” in the best way possible.

The age-defying — goodness, is she really 57?! — beauty adjusts her Christian Louboutins yesterday while flashing her million-dollar smile outside ABC’s “Good Morning America” studios in Times Square, where she was promoting her new role as Roxie in “Chicago.”

She confessed she was surprised by the gig, but said, “I wasn’t going to spend the rest of my life, you know, wondering, I woulda, shoulda, coulda — what if?”

She debuts tomorrow.