I feel this has some post processing, but most of that "misty" effect is due to the angle of the sun relative to the subject. The sunlight bleeds around the edges of the subject and creates that effect. It is generally something people want to avoid. I have had this effect ruin many shots when i try to photograph someone with sunset in the background. The effect of the "mist" washes out all details from the face. And most of the time, it is something i would want to avoid.
It looks good, in this example, because those are 2 beautiful people, in beautiful outfits in front of a beautiful landscape with a beautiful pose.
I get the exact same effect when trying to photograph my ugly friend in front of a boring landscape, and i mostly discard those photos.