He's not visible anywhere in XY after Floette returns to him. However, in between the story events of XY and Z-A, he goes onto establish Hotel Z within Lumiose City, with the intention of living out the rest of his life there with Floette. Due to the anticipation of Ange reawakening, he goes on to establish the Z-A royale with Quasartico to find the strongest Mega Evolution trainer deactivate the device.
So even though you can't find him after he's reunited with Floette in XY... he's probably working hard to set up his hotel.
In the five years following the events of X and Y, AZ purchases a property in Lumiose City and establishes Hotel Z, with the intention of living out the remainder of his life there alongside his Floette. Due to the recent activation of the ultimate weapon by Team Flare, AZ anticipates the reawakening of Ange, embedded deep within the Prism Tower, and warns Vinnie and Jett of Quasartico Inc. of the device's existence. Together, they later witness a disturbance at the tower resulting in the release of Mega Power. As a consequence, wild Pokémon are drawn to the city in droves, and some are forced to Mega Evolve on their own, a phenomenon that would come to be known as Rogue Mega Evolution. AZ warns Quasartico of the need to locate a trainer capable of Mega Evolving his Floette and using Mega Floette to deactivate the device.
Heeding his warning, Quasartico establish the Z-A Royale with the ulterior goal of locating the strongest Mega Evolution user in Lumiose City. They promise competitors that whoever reaches Rank A will be granted a wish, provided it is within the company's power to do so. Quasartico close Prism Tower and begin constructing a confinement structure to contain the Mega Power being emitted. During this time, AZ befriends a group of youths who begin to work for the hotel in exchange for room and board: Urbain/Taunie, Lida, and Naveen. Together, the youths form a collective known as Team MZ, with the hope of drumming up business at the hotel which sees few guests. They are soon recruited by Quasartico to assist in handling the Rogue Mega Evolution phenomenon, which the company have covertly been attempting to suppress for two years.
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