Jack had no idea who it would be. When he looked through the peephole, it looked sort of like Mere, but why would she be knocking? She had her own set of keys, and even her own entrance to the basement, so she wouldn't even need to come to the front door.
Still, he opened the door to see who it was. Dear god...he thought he might faint. There was no way in hell that this was his long lost (if by 'lost' you mean packed all her shit and bailed on him) sorta-wife/Mere's mother standing on his doorstep.
He leaned against the door frame and stared at her for a moment before speaking. "I think my eyes deceive me," he said with a chuckle finally. "Because it makes no sense as to who I am seeing right now. It's been a long, long time, Louise."