YOU SAID:

Once there was a cow who ate my little brother

INTO JAPANESE

かつて、私の弟を食べた牛がいた

BACK INTO ENGLISH

Once upon a time, there was a cow who ate my brother.

INTO JAPANESE

昔、私の弟を食べた牛がいました。

BACK INTO ENGLISH

There used to be a cow who ate my brother.

INTO JAPANESE

かつては私の兄を食べた牛がいた。

BACK INTO ENGLISH

There used to be a cow who ate my brother.