Cooper Koch let it all hang out — literally — during the prison shower scene in “Monsters: The Lyle and Erik Menendez Story.”

The 28-year-old actor, who plays real-life convicted murderer Erik Menendez in the buzzy Netflix series, revealed that he didn’t use a prosthetic for the full-frontal scene in the third episode.

During an appearance Monday night on “Watch What Happens Live,” the NSFW display was discussed in a segment that counted down the “top five most iconic full-frontal moments” in entertainment.

Famous nude scenes of Jude Law in “The Talented Mr. Ripley,” Daniel Radcliffe in Broadway’s “Equus,” and Sharon Stone in “Basic Instinct” were among those that made the cut.

But when host Andy Cohen mentioned Mark Wahlberg in “Boogie Nights,” Koch interjected: “Just to say, mine was not a prosthetic!”

“That was going to be my next question!” Cohen, 56, said. “Congratulations to you, Cooper. You’re very blessed, aren’t you?”

“Well-hung!” he replied.

Earlier in the show, Koch was probed about his fears of baring it all on camera.

“It’s not scary, I would say it’s just more uncomfortable at first,” the “Swallowed” star said. “And it’s very cold, especially in the shower.”

Since “Monsters: The Lyle and Erik Menendez Story” dropped last month, there’s been a renewed interest in the case and discussion around whether the brothers should still be behind bars.

The siblings, who brutally killed their parents in 1989 following years of alleged emotional and sexual abuse, have been serving life sentences since 1996.

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