At the end, we see Alan dropping Jake off at Judith's and then the exterminator leaves and he resembles Jake A LOT and Judith seems to really like him. Alan tells Charlie that the exterminator has been coming over to the house forever. Charlie starts to suspect that the exterminator may be Jake's dad and not Alan but can't believe Alan never seems to notice. Then he sees a delivery man and a mailman who Alan seems to know well and they both resemble Jake, too. Just like Jake, they both have big bellies and bad haircuts.
It makes you think that Judith is probably scamming Alan the way that woman was scamming Charlie. I mean Judith probably knows one of them is really Jake's dad instead of Alan but chose to keep saying that Alan is the dad because the other guys have pretty much dead end jobs that don't make as much money as a chiropractor like Alan does and we know Judith is a gold digger. I mean Judith probably married Herb because he makes more money than Alan does and figured she could get more money from Herb than she could off Alan's alimony.
I figured there'd be a conversation:
Alan: Do you honestly believe that Jake is not my son?
Charlie: Well, it would certainly explain a few things.
Alan: Like what?
Charlie: Oh, like...EVERYTHING.
It would because look at Alan and Jake, they don't look alike, they don't act alike, they don't even use the bathroom the same way. Alan enjoys peeing sitting down and Jake seems to miss the toilet a lot.
I figured that at the end of the series, Alan would find out that Jake's not his son and that Judith knew all along and scammed him. Then Judith would have to start paying back all the money that Alan spent on Jake and now Alan would be living the easy life that Judith was living when Alan had to pay her alimony. Jake would ask Judith who his real dad is and Judith would say that she does have it narrowed down and then those 3 guys would appear at the door all at once and say,"Hi Judith."