'Westworld' Creators Explain That Surprise 'Game of Thrones' Crossover (Exclusive)

'Game of Thrones' creators David Benioff & B.D. Weiss made a cameo on 'Westworld' and only ET has the exclusive behind-the-scene scoop!

Have you ever questioned the nature of your reality?

Well, if you happened to catch that Game of Thrones cameo on this week's episode of Westworld, we bet you are now!

On Sunday night's episode, GoT creators David Benioff and D.B. Weiss appeared in a short, but surprising scene -- and only ET has the exclusive scoop straight from the Westworld executive producers and stars about how this Westeros-inspired moment (and Drogon!) made it onto our screens.

What Exactly Happened in the Scene?

Approximately 38 minutes into "The Winter Line," the second episode of Westworld's third season, Bernard (Jeffrey Wright) and Stubbs (Luke Hemsworth) are walking through a glass-walled hallway that fans have never seen before. As the camera pans, we see swords and shields hanging from the walls while bloodied hosts wearing suits of armor are waiting to be repaired. (In fact, one of them looks eerily similar to The Hound!)

"What are we doing in park four?" Bernard whispers to Stubbs. "I thought the parks were shut down."

"They are," Stubbs replies. "These techs are just waiting to see if they get laid off."

As Bernard and Stubbs walk by, we see two techs sitting casually inside one of the glass rooms -- and they just so happen to be played by Game of Thrones' former showrunners Benioff and Weiss.

"I've got a buyer," Weiss' character says. "It's with some startup in Costa Rica."

"How the f**k are you going to get that to Costa Rica?" Benioff's character replies.

"In pieces, man," Weiss deadpans.

The camera pulls back to reveal Game of Thrones' most iconic character, Drogon, is sleeping soundly right behind them, but growls awake as the tech approaches the host dragon with a buzz saw.  

How Did This Game of Thrones Cameo Happen?

ET caught up with Westworld co-creators and executive producers, Jonathan Nolan and Lisa Joy earlier this month at the red carpet premiere in Los Angeles and the showrunners dished on the ultra-secret scene.

"Well, we're friends with Dan and Dave," Joy explained with a smile. "And we're fans of their work and we just wanted them. You know, George R.R. Martin always joked there should be a crossover between Westworld and Game of Thrones and, while that seems untenable, we knew we could do a little Easter egg with our pals -- so we brought them on and they did a good job!"

"Yeah, we had fun," Nolan added. "Jeffrey and Luke are in the scene, I was working with Tessa around the corner and everyone was excited to spend some time with them."

"I mean, we're really doing this show because what they did for television with Game of Thrones. They reinvented the medium," Nolan continued. "We couldn't be doing what we're doing if they hadn't made that show, so [this was] a little homage to them. And, as Lisa said, they've been great friends, very supportive and it was lovely having them on our set."

What Did the Westworld Stars Think of This On-Set Surprise?

ET caught up with a handful of the Westworld actors to get their thoughts on this HBO Easter egg!

"I was on set, but not participating," Thandie Newton, who plays Maeve, explained. "But yeah, they were sweet. They were sweet! It was like they were geeking out, you know? They got to be in one of their favorite shows, and Jonah and Lisa really admire their show, and it's an HBO family -- so yeah, it was really cute."

"OK, so I was really embarrassed because I've never seen Game of Thrones!" Tessa Thompson confessed. "So they were on set and I was like, 'Cool. I've never seen your show. I hear it's great!' They were lovely and they made me want to watch the show all the more, so I will finally watch Game of Thrones at some point in my life."

Meanwhile, Hemsworth, who was actually in the scene, admitted that he has no recollection of seeing the GoT showrunners on set. 

"You know what? I don't remember them being there," he said with a chuckle. "So either I was really in the moment or they weren't there."

"There was definitely no dragon there!" the Aussie actor added. "Pretty sure it was just a silver ball or a puppet or something, but yeah, that's awesome. Let's bring more of that! This is the Big Little Lies world and this is the Barry world."

As for Westworld's leading lady, Evan Rachel Wood, she's hoping this crossover will make fans think long and hard about the nature of their TV reality.

"Is Game of Thrones just another world in Westworld?" she asked with a coy laugh. "Time will tell. Who knows?"

Westworld airs Sundays at 9 p.m. ET/PT on HBO.