EXCLUSIVE

O.M.G. ... JON SNOW IS TOTALLY DATING YGRITTE!!!!!

TMZ has obtained a photo of "Game of Thrones" star Kit Harington on a dinner date with his smokin' hot redhead co-star Rose Leslie in London earlier this month.

The two were pictured holding hands and smiling at each other ... and sources inside the Rossopomodoro restaurant tell us they were even sucking a little face during the meal.

For those unfamiliar with "GoT" ... Kit's character and Rose's character have CRAZY sexual chemistry on the show ... with Ygritte constantly teasing Jon in a sexual manner. They even fell asleep together once, but it turned out to be a trick and she ran off ... lured him into a trap and got him captured by the Wildlings. They still might eventually bang though.

Still ... if Ned Stark found out about this, he would lose his head.