YOU SAID:

I still know what did you did last summer

INTO JAPANESE

私まだことを知っていた去年の夏

BACK INTO ENGLISH

I already knew that the last summer

INTO JAPANESE

私がすでに知っていた去年の夏

BACK INTO ENGLISH

I already knew last summer

INTO JAPANESE

私は既に昨年の夏を知っていた

BACK INTO ENGLISH

I already knew last summer