This is the 7338th most frequent Japanese word.
亡くなる
"亡くなる" means "to pass away" or "to die."
In this sentence, "亡くなりました" is used as a respectful way to indicate someone's passing, commonly referring to others in a polite context.
彼のおじいさんは昨年亡くなりました。
His grandfather passed away last year.
Here, "亡くなってしまった" expresses the sorrowful occurrence of someone's passing, in this case referring to a pet, showing a personal and emotional context.
犬が老衰で亡くなってしまったので、とても悲しいです。
I am very sad because our dog passed away due to old age.
This usage of "亡くなりました" reflects the loss of lives in a historical or general factual context, often used in discussions of past events.