"Because the country is beautiful, because the Northern Lights are magical, and because it was there that I fell in love," he said.
"If you're already attracted to someone, and then they play your love interest in the show, it's becomes very easy to fall in love."
So telling her was a no-brainer. It's the other person he told which is the shock.
Speaking on The Tonight Show, Harington revealed he shared the secret with a cop who pulled him over for driving too fast.
"I was going over the speed limit and I feel the sirens go off behind me and this policeman comes up, pulls me over," Harington said.
"He said, 'look, there's two ways we can do this: You can either follow me back to the police station now and I book you in or you can tell me whether you live in the next series of Game of Thrones.'"
So Harington told him and the policeman's response was: "On your way, Lord Commander".