I've announced a one shot in a Discord server, and prospective players have contacted me to join it. We don't know each other.
I asked them to prepare their character before the session, and it turned out that one of the player has not yet submitted their character because he is still writing the backstory.
While usually I'm very appreciative of an extensive backstory of a character, I don't plan to use them for this particular one shot. I don't plan this scenario to be RP-heavy. However, I don't want to break his attachment to this character or break his immersion in the world. I just want to make him know that we won't be using it for the one shot.
How can I tell him we won't be using any background story for the one shot, without ruining his excitement in writing the background?
Note: Other players didn't submit any background story, just background.