It wasn't that he was surprised... but Fred was surprised. The nose and sneer just sealed the deal. He was looking at a female Snape and since, as far as he knew the Great Bat had no siblings.
"Funny," he muttered, "I always figured he sprang forth, fully grown from the nightmares of small children."
"You've already met my family. Probably." There were enough of them to go around. "And you mentioned the wedding first." The wedding in which he was spiking the punch, no matter what anyone said. They'd need it to get through the ceremony and reception.