Mona May had no designs on becoming a movie star.

But as the costume designer of cult classic “Clueless,” she covertly slayed a scene with Alicia Silverstone’s Cher Horowitz— as if being on camera were her true calling.

“It’s a really great-kept secret that I’m in the movie,” May exclusively told The Post of her blink-and-you’ll-miss-it cameo, proposed by director Amy Heckerling, as Cher’s massage therapist in the 1995 teen comedy.

“It was a last-minute thing,” laughed the style savant, lionizing Heckerling for cinematically immortalizing her in the film, which is celebrating its 30th anniversary this year. 22

“Amy was, like, ‘Oh, my God, we gotta do this masseuse scene. We need somebody Eastern European — let’s get [you] in there,’” recalled May, who was born in Indi

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