Timothée Chalamet had a pretty good reason to let Kylie Jenner fly solo at the Met Gala ... his NBA team was playing an important playoff game, and he had to watch!!!
The actor, who is a big Knicks fan, was nowhere to be found at Monday's Met Gala in New York City ... instead, he was tuning in to watch the Knicks play the Boston Celtics in Game 1 of their series.