Hi, Tim!
I am quite busy this week, but coping.
Thank you for the comment. You are right about the Latin phrase.
According to some historians, Caesar said the phrase in Greek "Και συ, τέκνον;" which means "You too, my son?" or "You too, young man?".
Souetonius mentioned it in "Divus Iulius"

But I believe Shakespeare preferred Latin instead of Greek, because Latin were most frequently used in his era.

Loved this gif