あの人にはあきれてしまった。

that (someone or something distant from both speaker and listener, or situation unfamiliar to both speaker and listener)

man; person; human being; mankind; people; human (Homo sapiens); humans as a species; character; personality; man of talent; true man; another person; other people; others; adult

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

to be amazed; to be shocked; to be astonished; to be astounded; to be disgusted