Clemont's Dedenne appeared in a forest outside of Lumiose City. As soon as
Bonnie saw it she thought it was cute and wanted to keep it but because she wasn't a Pokémon Trainer, she tried to convince her brother to capture it for her.
Bonnie noted that it wasn't afraid of humans and it got along with
Ash's Pikachu quickly since they're both Electric types and they communicated with electricity.
Clemont initial attempt to capture it was not successful though. A few days later though, the same Dedenne reappeared as it had been following them the whole time they had been traveling. This time though
Clemont was successful in capturing it. It really seems to like the Pokémon food that
Clemont and
Bonnie give it.