Penny is David's Father by Matthew (MJFV1)

LOST has always been one to drop hints at every turn. With that said I believe in the ALT Timeline, Penny is the mother of David, Jack's son.

I believe the first hint at this is the fact David is a lot like Daniel Faraday/Widmore.....a possible hint at his ties with the Widmore family. David not only played the piano at a young age very well, but played the same song Faraday played earlier in the series.

Another hint could be the running at the stadium. We now know Desmond wasn't running there at the time Jack needed to run after fixing Sarah. We also know that in the ALT Timeline, Penny was an avid runner there.

I suspect when Jack ran at the stadium he ran into Penny, instead of Desmond resulting in Jack & Penny to become an item & Jack never going with Sarah.

Another small hint could be when Jack was offered a drink. The drink he was offered was McCutcheon, the same drink commonly linked to the Widmore family. Perhaps it is another hint at a possible relationship between Penny & Jack.

We know David's mother was not revealed, there were no hints at who it could have been & can think of no way it wouldn't be Penny who is David's mother.