Hear me out here if Kris is a dude and Asriel is a dude then we could say that Kris is Asriel because

1 they have the same coloured shirt and pattern

2 Kris after getting a soul acted differently and Asriel after he was made into a flower acted differently

3 flowey knows almost everything about each Undertale character and probably has information about gaster and Kris is probably working with gaster

4 we have seen some character development from Kris and Asriel

5 the reason toriel divorced asgore is because he hid the fact that Kris is Asriel confirmed from an interview with Toby fox

What Toby fox said in the interview

"Anyways Kris is Asriel and asgore divorced toriel because gaster gave omori depression"

6 in another interview Toby fox said this

"Please stop quoting me on things I never said"

Wich is a clear foreshadowing of Kris being asriel