Marcus Junius Brutus's father was Marcus Junius Brutus, pleb tribune and founder of Capua (yes that Capua of Spartacus fame). He was later adopted by Quintus Servilius Caepio.

The only known biological son of Gaius Julius Caesar was his and Cleopatra's son Caesarion. His only adoptive son was Octavian, later known as Augustus.

I thought Brutus was his son and his last words supposed to be “tu quoque fili”

Caesar's last words, according to some accounts, were "Kai su, teknon?" - "You as well, my son?"

It's generally accepted that "my son" is meant figuratively here, as a younger man whom he considered affectionately, but some argue that Brutus was literally Caesar's illegitimate son from an affair with his mother.

This is generally considered a fringe theory, as it would require Caesar to have been in his mid-teens when he seduced Brutus's mother, but is not completely impossible.