Sophie Turner was a guest on Wednesday's Conan, and demonstrated a drinking game she played with her X-Men: Dark Phoenix co-stars when they weren't filming.
"We played this brilliant game called Tequila Slaps," the Game of Thrones star told O'Brien and his co-host, Andy Richter, before pulling out a bottle of Don Julio 1942tequila. "I really want to play this game with you."
The 23-year-old actress poured herself and the guys each a shot of alcohol and then instructed O'Brien to stand with his drink.
"You're nice and tall, I like that," the 6-foot-4 host complimented Turner, before inquiring how much time he had before she would slap him.
Just as the glass hit his lips, Turner hauled off and slapped O'Brien across the face! Needless to say, he was in shock, and Joe Jonas' wife was immediately apologetic.
"I'm so sorry!" she said while hugging the 56-year-old host.
After coming to terms with what had just happened, O'Brien exclaimed, "Wow! That was a fantastic slap! ...Man, you don't screw around."
Turner said her and her Dark Phoenix co-stars go "really, really hard" when they play the game, noting that she once had a "purple hand mark" after being slapped.
"Now, are men slapping you in this game?" Richter inquired.
Turner admitted, "I mean, you can give them permission, yeah."
Richter quipped, "Wow, that's quite a workplace."
When Turner tried again to apologize to O'Brien, he insisted, "No, don't be sorry. That was fantastic. I can dine in on that for years. ...That's the most exciting thing that's happened to me in a long time."
Before she slapped a beloved late-night host, Turner hit the red carpet for the Hollywood premiere of Dark Phoenix -- and ET was there!
Check out our exclusive interview with the fierce actress!