Wasn't Brutus like twenty when the relationship between his mother and Julius began?
AFAIK this whole thing only began with Shakespeare. Patricide makes things more dramatic.
In the HBO series Rome, it implied Caesarion was not been Caesar's son. I realize the show took some major historical liberties but what's the historical background on this if any?
Before or after Octavius had the boy killed?Caesar was old when he met Cleopatra, but no one ever claimed that Caesarion wasn't the son of Caesar.
EDIT: Nevermind that last part, one of Octavians supporters, Gaius Oppius, wrote a pamphlet that it was impossible for Caesarion to be the son of Caesar.
Before or after Octavius had the boy killed?
"There cannot be two Caesars."Extremely likely to be Octavius' propaganda, though.