Falling in love, Jon and Daenerys finally succumb to their growing feelings for each other and have sex. Neither of them is aware they are related by blood or that the Night King has revived Viserion as a wight.
Throughout the series, Dany came across many people, 4 of whom were in love with her: Drogo, Ser Jorah, Daario Naharis, and Jon Snow. Drogo was killed off at the end of season 1 by wound and black magic. The way he was protective of her gave us a glimpse of their relationship.