October 9, 2017 11:00 AM EDT

When it comes to pranks, Game of Thrones actor Kit Harington is not messing around.

His newly-announced fiancée Rose Leslie learned this the hard way last April, when Jon Snow‘s alter ego took his macabre sense of humor to the next level, playing a prank on Leslie that she would not soon forget. (Maybe all that time on the Thrones set fighting off decomposing, reanimated corpses is rubbing off on him — and desensitizing him to gruesome scenes.)

The prank: a severed head modeled in his likeness, placed casually inside the refrigerator for her to unwittingly discover. The reaction: screams, tears, utter despair. In a new appearance on the Jonathan Ross Show, Harington shared the video he took of Leslie’s horrified response. While funny in retrospect, it wasn’t quite a win for Harington.

“My family does April Fool’s. Her family doesn’t do April Fool’s,” Harington explained. “After that, she was in tears. And I was there going, ‘April Fool’s.’ It didn’t go down well.” In fact, although it was a successful prank, it doesn’t sound like he’s converted Leslie to the joys of April Fool’s in the slightest. “She pretty much told me if I did it ever again, that would be it, and I think that’s marriage included,” he said.

The couple, who met on the Thrones set while filming in Iceland, announced their engagement at the end of September.

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Write to Raisa Bruner at raisa.bruner@time.com.

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