Pokémon Sun and Moon - Lusamine and Mohn's wedding photo

We saw him in Lusamine's wedding photo, and Gladion talked about him with Lillie in the most recent episode. His story in the anime is that he died in an accident while researching Ultra Wormholes. Gladion was too young at the time to know all the details, and Lillie is too young to remember him at all, but they assume that he's dead instead of just missing like in the games.