Who was the father of Portia?

Portia Catonis (70 BC-43 BC), usually known simply as
Portia, was the second wife of Marcus Junius Brutus, the friend and assassin of Julius
Caesar. Portia was the daughter of Marcus Porcius Cato Uticencis and his wife, Atilia.
Portia's suicide is also well known, supposedly as a result of swallowing live, burning
coals. Before her marriage to Brutus, she wed an ally of her father, Marcus Calpurnius
Bibulus. They had a son, Lucius Calpurnius Bibulus, but there is some doubt that Portia
actually gave birth to him, since she would have been between the ages of 11 and
17.