The 32-year-old actor, who met his wife Rose Leslie when she appeared as Jon Snow’s love interest Ygritte in the fantasy drama, said that there was an “element of weirdness” to filming romantic scenes with Clarke.
Discussing the burgeoning romance between his character Snow and Daenerys Targaryen (played by Clarke), Harington told the Daily Mirror: “Emilia and I had been best friends over a seven-year period and by the time we had to kiss it seemed really odd.
“Emilia, Rose and I are good friends, so even though you’re actors and it’s your job, there’s an element of weirdness when the three of us are having dinner and we had a kissing scene that day.
“She’s wonderful and I love Emilia and I’ve loved working with her. And it’s not hard to kiss her, is it?”
The star, who tied the knot with Leslie last summer, said that it felt “awful” to watch his wife kiss other actors on screen.
“I went to see a movie Rose did called Honeymoon where she spends half the movie snogging with my friend Harry Treadaway,” he told the paper. “About five minutes in I had to close my eyes because I couldn’t stand it.
“I was sitting between Rose and Harry and it was awful. I was watching them play a couple on a honeymoon and it wasn’t pleasant, because she’s an incredible actor and I was watching her thinking that she really loved this guy.”
Harington previously revealed that he had tried to keep the outcome of the show’s finale from Leslie.
“Spoilers are one of those things in my daily life which I just have to avoid,” he told Standard Online. “Me and [Rose] and my friends all have an understanding now, which is that you don’t really want to know, even if you push me too hard.”
Game of Thrones season eight episode one is currently available to stream on NOW TV. It will be repeated tonight at 9pm on Sky Atlantic.