Did he even have any? Probably not! And if he did, it was in Greek!
“Roman authors claim that Caesar did not speak…Plutarch wrote that Caesar did not utter a word but that ‘when he saw Brutus had drawn his dagger, he pulled his toga down over his head and sank.’”
“Appian described Caesar’s last actions as ‘he at last despaired, and veiling himself with his robe, composed himself for death and fell at the foot of Pompey’s statue.’”
Cassius Dio recorded that “Caesar was unable to say or do anything but veiling his face.”
Nicolaus of Damascus wrote that: “he fell, under many wounds, before the statue of Pompey.” No mention of “Et tu, Brute?”
That leaves us with Suetonius: “As he took his seat, the conspirators gathered about him as if to pay their respects, and straightway Tillius Cimber, who had assumed the lead, came nearer as though to ask something; and when Caesar with a gesture put him off to another time, Cimber caught his toga by both shoulders; then as Caesar cried, ‘Why, this is violence!’ one of the Cascas stabbed him from one side just below the throat. Caesar caught Casca’s arm and ran it through with his stylus, but as he tried to leap to his feet, he was stopped by another wound.”
“When he saw that he was beset on every side by drawn daggers, he muffled his head in his robe, and at the same time drew down its lap to his feet with his left hand, in order to fall more decently, with the lower part of his body also covered. And in this wise he was stabbed with three and twenty wounds, uttering not a word, but merely a groan at the first stroke, though some have written that when Marcus Brutus rushed at him, he said in Greek, ‘You too, my child?’”
So Suetonius tells us he did not say anything as he died but only as he realized he was under attack he said that “Why, this is violence!” If he did say something as he died such as “you too, my child?” – He said it in Greek! It seems that the whole “Et tu, Brute?” – that’s the Caesar of Shakespeare not from the actual sources!
Sources:
Suetonius, The Lives of the Caesars
Ancient Rome: Facts and Fictions by Monica M. Bontty
shadowsofconstantinople.com 