Kaley Cuoco and Johnny Galecki Get Crazy in Behind-the-Scenes Photo from The Big Bang Theory

Well here’s a Big Bang Theory scene fans never expected!

On Thursday’s episode of the hit CBS sitcom, Sheldon (Jim Parsons) had a nightmare where he saw friends Penny (Kaley Cuoco) and Leonard (Johnny Galecki) dressed in bondage gear in their own personal sex dungeon.

It was a laugh-out-loud moment on the show. And on Instagram, Friday, Cuco gave fans a behind-the-scenes look at the making of the moment — in a scandalous, eye-catching shot!

The 30-year-old actress shows off her cleavage for the camera in pic, leaning forward with her mouth open while wearing a red corset, black shorts, a fishnet stockings. Costume designers accessorized the outfit with a black hat, mesh gloves and black chocker — oh, and a leather whip, of course.

Looking serious while standing next to her in the still is a shirtless Galecki, 41 — who wears a black leather bondage harness top with matching leather briefs and chaps. He also holds an S&M toy in his hand.

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“#bts of last nights @thebigbangtheory__ #kaleyspolaroids #corsettook15minstogeton @sanctionedjohnnygalecki,” Cuoco captioned the Instagram shot.

The two’s characters tied the knot on-screen during the season 10 premiere. But off-screen, they’re very much best friends despite quietly dating for two years (they split in 2010).

Cuoco has been hot and heaving with her equestrian boyfriend Karl Cook — whom she met after split from tennis player Ryan Sweeting in September 2015 after 21 months of marriage.

She and Cook recently made their red carpet debut at the Longines Masters Los Angeles Gala.