The pop star shed her green wig and baggy sweaters and swapped them for something a little more skimpy and steamy for the upcoming June issue ... and it's just about the most jaw-dropping thing we've seen in a good while.

BE looks like a pinup model from the '20s and/or '50s -- and yes, there are big-time echoes of Marilyn Monroe here ... at least in our eyes. Indeed, she's achieved bombshell status.

Now, we've seen Billie without the green hair of late and even without the loose clothing too -- but we haven't ever seen her quite like this ... where she's showing off her physique for a magazine shoot. There's something to be said there too, which Billie did in her interview.

She talked about body image issues -- and not necessarily ones she had for her herself ... but ones the media placed on her as she was thrust into the spotlight over these past couple years. Billie posted a quote of hers from the Vogue issue, and she talks about the freak-out that some outlets had when Billie stepped out in anything other than her signature look.

Billie says, "Suddenly you’re a hypocrite if you want to show your skin, and you’re easy and you’re a slut and you’re a whore. If I am, then I’m proud." She adds, "Me and all the girls are hoes, and f*** it, y’know? Let’s turn it around and be empowered in that. Showing your body and showing your skin -- or not -- should not take any respect away from you"

In other words ... her message seems to be, do whatever the hell you want, and look however the hell you want, regardless of what others expect. Good advice right there.