>>31905407Seeing how he and Bonnie looked at eachother when Serena told Ash she was her goal I suppose he had already figured it out, my guess is that it happened sometime between the dance episode and the Snowbelle episodes. And one has to wonder if Clemont and Bonnie leaving Ash and Serena alone during XY&Z45 wasn't completely deliberate and not just because they "had to do something at the gym".
