Colin Farrell recalls 'monumental' moment with son who has rare genetic disorder

— -- Colin Farrell's latest movie role as a torn father has him opening up about his real-life fatherhood journey.

In "The Killing of a Sacred Deer," Farrell portrays a heart surgeon and a father of two who has to make a tough choice that will affect his family forever. The horror-thriller, which also stars Nicole Kidman as his wife, premiered this weekend at the Toronto International Film Festival in Canada.

When talking about his journey as a father, he could recall only a happy moment about his son with model Kim Bordenave, 13-year-old James.

He was born with a rare genetic disorder called Angelman syndrome, a developmental disability, characterized by seizures, jerky movements and sleeping problems. There is no known cure.

"When James took his first steps a couple weeks short of his 4th birthday, it was pretty amazing and humbling to see," Farrell told People magazine.

Farrell, 41, also has a 7-year-old son, Henry, with Polish actress Alicja Bachleda-Curus.

The actor said that a child's first steps are remarkable for every parent, but for him and his family, it meant something even more.

"People talk about the children taking the first step. It’s obviously a monumental moment, and it's been represented in film," Farrell said. "But to be told your child may never take the first step and then see those first steps is just kind of a different sport altogether."

He began talking publicly about his son's struggles and triumphs after attending the 2007 Special Olympics in Shanghai, he revealed in InStyle magazine in 2012.

He said, "I decided, after consulting with James' mother, that I wanted to talk publicly about the pride and joy I had in our son."

"We share in the smallest victories — the first words at age 6 or 7, being able to feed oneself at 9 and getting the seizures under control," Farrell added. "When you're the parent of a child with special needs, it's important to feel that you're not alone."