He and his twin sister Vivienne make up the youngest children in the Jolie-Pitt family captained by their parents, renowned actors Angelina Jolie and Brad Pitt.
He was born in 2008, six years prior to his parent's marriage in 2014.
He was named after his father's maternal grandfather Hal Knox Hillhouse.
In addition to his twin sister, he has four other siblings: Maddox, Pax, Zahara, and Shiloh.
His uncle, James Haven, is an actor like his parents.