As fans can recall, in the Season 2 premiere of the HBO series, James' character Cameron strips down naked while changing into a swimsuit.
During an appearanon Friday night's episode of "The Tonight Show Starring Jimmy Fallon," James, 37, revealed the hilarious story behind the "pee-pee scene," confirming that he was, in fact, wearing a prosthetic.
Bringing up the scene, Fallon cracked, "People thought it was the Loch Ness Monster. Good for you, by the way! Oh my god!"
"Please stay seated. I don't want you getting exhausted. I don't want you getting tired leaving or standing up," he quipped as James laughed. "Stay in your chair. We'll wheel you outta here."
"I can't breathe sometimes because of the weight of it," James jokingly replied, continuing the gag, before he shared details about the scene.
"The truth of it was, so, you know, you go into these scenes and you have a conversation with the director and the producers and they go, 'Okay, for this, we're going to use a prosthetic,'" he recalled. "And you say, 'Okay, that sounds good.'"
Fallon then asked for confirmation that the British actor wore a fake penis, to which he replied, "Yeah, it's a pee-pee prosthetic." In response, a relieved Fallon quipped that the revelation "makes so many men feel so good right now."
James recalled the conversation he had with the show's makeup designer about the prosthetic, noting that he wanted his character to be a "Regular Joe." However, as people who've seen the scene can tell you, that's not what it turned out to be.
"I said, 'Honestly, I just want it not to be distracting. He needs to be Regular Joe, 'cause the scene's… you know, it's not about the pee-pee -- it's about power play and sex," James recalled to Fallon. "It's about whether he did it deliberately or whether it was an accident and what that means and all that kind of stuff.' And she says, 'I got you. Yeah, I got you. Regular Joe.'"
"We get to set and she's got, like, a hammer or something," he continued as Fallon and the audience burst into laughter. "I mean, it's bigger than that. It's like she stole it off a donkey in the field. The thing is ginormous. And me and the director, Mike White, are sitting there going, 'That's… average, is it?'"
"We're calling our respective partners being like, 'I'm so sorry,'" James quipped, adding that the prosthetic was "nine inches flat and about four inches wide."
"We were like, 'What the hell is that?'" he said.
The "Divergent" star went on to note that a "Tonight Show" producer asked him if he kept the prosthetic. "I was like, 'No, I don't have it!" James said, before joking that it sleeps next to him.