Theory - Is Sans from Undertale or Deltarune?

Since Deltarune Chapter One came out, one question has been going around a lot - where does Sans originate from? Well today I will be seeing if I can answer that question.

First off, when we see Sans, he's in front of a familiar looking building. It's Grillby's, but "Grillby" is rubbed out and "ans" is written after the "'s". The most likely reason is that Sans brought this to Deltarune from Undertale, since we don't hear of Grillby and there already is a bar/cafe in town.

When we talk to him, he says that he's new to town, with a wink. Though many have interpreted the wink to mean that he's not new, I think he means that we've met before (in Undertale, of course). Since Deltarune seems to be going in a direction where Kris is forced to go along a certain path in the game (and how the player has all of the control and yet none of it at the same time), this would make perfect sense.

This is a small theory, but regardless of its size it's a theory and it does matter.

Unlike your choices in Deltarune...

An interesting thing to note, however, is the use of Sans’ bedroom doors in Deltarune’s Dark World, especially since Kris themself hasn’t met Sans beforehand… But we have.

But then there's Sans' lab. Everything seems to be pointing toward Sans originating from Undertale except for that picture in his lab with "Don't Forget" written on the back. I think the three people may be Kris, Susie and Noelle (or Ralsei), which may be pointing to Sans originating from Deltarune, since this is in his lab. But I think that this is a simple Easter Egg for Deltarune, like Clam Girl. But instead of requiring a certain amount of FUN value, if requires the player to follow a certain set of instructions.

Thank you for checking out this theory.