The secret invisible undies all the celebs are wearing on the red carpet.

Ever looked at celebrities on the red carpet in daring cut-out or seethrough gowns and wondered how on earth they don’t have visible panty lines?

We finally know the answer.

A Hollywood costume designer has finally spilled the beans and we’ve already added four pairs to cart.

The secret is to go Commando – the brand, not the action that is.

In a piece for The Cut, designer Alison Freer said she swears by the cotton blend microfibre boyshorts by Commando, $41, which she was recommended after she got a rip in her leggings mid-Pilates class - while wearing nothing underneath to avoid VPL.

"They are whisper thin, lay perfectly flat like a second skin, and are absolutely invisible underneath every single pair of pants I own," she wrote.

" If you’ve ever wondered what the stars on the red carpet were wearing underneath those sheer, unforgiving gowns, the answer is almost certainly a pair of Commandos."

Image: Bare Necessities

Made in the United States out of nylon and spandex, their "naked", elastic and trim-free construction means they're essentially wedgie proof and won't move, dig in or bunch up when you start to move or even sweat.

It's not just for the red carpet either - they'll do the same under any tight or light-coloured clothes or tailored pants.

Listen: Remember that time Chrissy Teigen almost had a full vag situation on the red carpet? Post continues.

Boyshorts not your thing? They also have a range of styles from bikini briefs to high waisted.

Your best best at purchasing them in Australia is from Bare Necessities, who now ship down under. The undies aren't exactly cheap at $41.43 a pair, but some would argue that a wedgie and noticeable undie outline-free day is pretty priceless.