、。
Seeing her alluring figure, he was completely captivated.
Literal
Her bewitching figure [object-を] seeing, he [topic-は] completely infatuated became [regrettably-てしまいました].
悩ましげな ('seeming bewitching/troubled') uses ~げ (appearance suffix) on 悩ましい ('bewitching, provocative'). 姿 ('figure, form') is a versatile word. すっかり夢中になってしまいました ('completely became infatuated [and that was that]') stacks すっかり (completely) + 夢中 (engrossed/infatuated) + てしまう (regrettable completion). The polite form (しまいました) adds a storytelling tone.