Why was "Et tu, Brute" said?
Brutus was Caesar's best friend. Mark Antony reminds the citizens of that fact in his funeral oration.
For Brutus, as you know, was Caesar's angel.
Judge, O you gods, how dearly Caesar loved him!
This was the most unkindest cut of all;
For when the noble Caesar saw him stab,
Ingratitude, more strong than traitors' arms,
Quite vanquish'd him.
The line "For when the noble Caesar saw him stab" was probably intended to be recited with a strong emphasis on the word "him."
For when the noble Caesar saw him stab
According to Shakespeare's version of the assassination, Caesar tries desperately to save himself when the conspirators converge around him and began stabbing him repeatedly with swords and daggers. But when Brutus, who has been hanging back, steps forward and stabs him one time, Caesar gives up all resistance and says:
Et tu, Brute? Then fall, Caesar!
He is saying, in effect, that if even his best friend Brutus is against him, he has no chance of saving himself--and doesn't even want to save himself. (At this point he may remember the Soothsayer's warnings to "Beware the Ides of March.") The Latin words "Et tu, Brute?" ("Even you, Brutus!") are meant as a reproach as well as an expression of Caesar's realization that he is doomed. Of course, it is important to remember that while Shakespeare has Caesar say this line in the play, there is no actual historical evidence to suggest that those were Caesar's real last words.