Mel Brooks' son, Nicky Brooks, is sharing a lesser-known side of his famous father ahead of the director's monumental 100th birthday. "My dad tended to express anxiety, stress through anger, and he became a very angry person, very volatile mood-wise," Nicky recalls in the upcoming two-party documentary Mel Brooks: The 99 Year Old Man!, premiering January 22 on HBO, per Entertainment Weekly. "It was difficult for my mom trying to raise these babies, and I think it just reached a point where my dad was just frankly so difficult to live with," Nicky continues in the documentary.