What "...しもーたん" could mean?

Question

I came up with this sentence while reading manga:

何であんなふうに育ってしもーたん。

Context: That's what the grandfather says after his grandson exits the house without telling anyone.

育って - I believe it's the te-form of the verb 育つ, which means (from Jisho.org):

1. to be raised (e.g. child); to be brought up; to grow (up)

I don't know what "しもーたん" is. But from my research I gathered that しも could be a grammatical element in archaic Japanese (a sort of intensifier similar to nothing but, even, necessarily, etc) and looking at Jisho.org, たん could be an honorifc but that doesn't make sense since there is no character called しも.

My second guess is that しもーたん could be a contraction for something else, which I cannot guess.

Answer 1

しもーた is a variant of しもうた, which is a Kansai dialectal version of しまった used with an undesirable outcome. See the links posted by broccori. ん at the end of the sentence is explanatory-の/ん used to seek clarification. This type of sentence-end の commonly turns to ん in casual western speech (e.g., 好きなの? → 好きなん?).

何であんなふうに育ってしもーたん。
= 何であんな風に育ってしまったの？

Why did he grow up like that?