Slowpoke and shelder

[Kalosfan296]

If somebodys shelder evolves another trainers slowpoke who keeps the slowbro?

[Petzbreeder]

Such an occurance has never happened in the Anime before, as far as I'm aware. Maybe the Shelder is automatically released from the Pokeball of the other trainer when it bites Slowpoke's tail. I'd imagine Slowbro's trainer is the one who would keep it.