Writer Steven Knight has revealed he thought “Game of Thrones” was a kids show until he cast one of its actors in his own series. Knight, who’s perhaps best known for creating Cillian Murphy-starrer “ Peaky Blinders ,” was speaking at the Royal Television Society conference in London, in conversation with BBC journalist Katie Razzall when he made the admission. He recalled how his young son was obsessed with “Game of Thrones,” asking for a DVD boxset for Christmas, which Knight was happy to provide having seen it featured dragons.

It was only when he came to cast “Game of Thrones” alum Aidan Gillen in “Peaky Blinders” he realized the George R. R. Martin-created series had more adult themes.

When someone suggested Gillen for “Peaky,” they told Knight that he plays the brothel keeper in “Game of Thrones.” Knight responded in shock: “What are you talking about? It’s a kid’s show!” Gillen played Lord Petyr Baelish in the HBO fantasy series before stepping into the role of Aberama Gold in “Peaky.” He’s also appeared in “The Dark Knight Rises,” “Mayor of Kingstown” and the “Maze Runner” franchise.

Knight shared some “Peaky” memories during the conference, including that he first came up with the idea for the Birmingham-set show in the 1980s and pitched it to a U.K. broadcaster although it didn’t work out.

“I started off writing it as a novel then I presented a treatment to Channel 4,” he said. “I’m glad it didn�.