it was in the episode when we saw jack's father and ana lucia going to visit the house in australia to see his daugther...
but it seemed from the episode that neither claire nor jack are aware of the connection...
only we are... (as is true of many of the connections - the characters themselves are unaware)..
we also thought that Jack wouldn't want to see aaron due to guilt....either that because of him, claire died or couldn't get off the island and is now being held by Ben (it seems from the sayid episode that sayid is killing people for Ben because Ben is holding other survivors hostage on the island)..