John Cena Undergoes Quick Wardrobe Change After Naked Oscars Moment

John Cena went from ass-naked to looking like a good old-fashioned Greek philosopher in record time at the Oscars -- and the wardrobe change was actually caught on camera.

The wrestler-turned-actor was on hand Sunday for a pretty cringe-worthy bit where he was supposed to run across the stage naked for the Best Costume Design category ... which ended with JC shuffling across the stage with the winner's envelope covering his privates.

The whole gag here was that John was in his birthday suit, and he was there to highlight the best costumes in movies -- something Jimmy Kimmel had to come and help him with.

Once the screen was overtaken with the nominee montage and it flashed back to Jimmy and John onstage -- the WWE star was suddenly in a toga-like getup ... and it happened fast.

As it turns out ... it was something people BTS had to rush out and assist with in a matter of seconds -- which was caught on camera by someone at Vulture. The room went dark at this moment -- which we didn't see in the broadcast -- and John sure looked nude.

Funny enough, he's actually the 2nd "naked" famous buff dude on TV this weekend -- Josh Brolin stripped down as well during his 'SNL' hosting gig, albeit leaving his undies on.

Here's to the hunky old guys showing off what their mama gave them ... cheers.