Colin Farrell opens up for the first time about life with his 20-year-old son, James, who has a rare debilitating disorder called Angelman Syndrome, and why he’s starting a foundation to help adult children with similar disabilities prepare for greater independence. Read this week’s PEOPLE cover story at the link below. | 📷️: Cliff Watts

Like most parents, Colin Farrell was understandably proud when his older son James took his first steps. But for the actor, and especially James, the moment was all the more sweet.

Having been diagnosed with Angelman syndrome, a rare neurogenetic disorder, when he was 2½-years-old, James, now 20 (whom Farrell shares with an ex, model Kim Bordenave), hadn’t been hitting typical benchmarks. “He couldn’t sit up. He wasn’t crawling. I think he was a year and a half when we took him to get really checked out, and he was diagnosed as having cerebral palsy,” says Farrell, 48. “It was a common misdiagnosis because it shared a lot of the same characteristics.”

Two weeks short of James’s fourth birthday in their home at the time, his occupational therapist came up to Farrell and said, “’James has something to show you,'” the actor recalls. “I knew they were working on walking. And I stood over there, and she let him go, and he just came to . . . [he pauses to collect himself] I mean, it was so profound. It was magic. I’ll never forget just the face of determination on him as he walked toward me. He took like six steps, and I burst into tears.”

Farrell allows that a lot of parents of children who have Angelman syndrome are told their child might not be able to walk, “so to see those first steps was just . . . I’ll never forget it. It was so overwhelmingly beautiful.” James “has worked so hard all his life, so hard,” he adds. “Repetition, repetition, balance, his jerky gait. When he started feeding himself for the first time, his face looks like a Jackson Pollock by the end of it. But he gets it in, he feeds himself beautifully. I’m proud of him every day because I just think he’s magic.”

Now, the actor is launching the Colin Farrell Foundation to help support adult children with intellectual disability through advocacy, education and innovative programs. “We want to take a good look at residential potential for families with young adults who are ready to go out into the world and have a greater sense of community and connection,” he says.

“It’s really important for James and for all of our kids to feel like they are wanted, to feel like they’re part of the community. Not just out of charitable endeavors or being nice and doing the right thing, but out of a sincere desire to engage and learn about each other,” Farrell adds. “They have earned the right to have a greater degree of individuality and autonomy of life and a greater degree of community.”

Though James is nonverbal, Farrell trusts in his intuitive knowledge of his son when it comes to knowing what he would want. “I have to make a call based on knowing James’s spirit and what kind of young man he is and the goodness that he has in his heart,” the actor says. “I choose to believe that if he knew us doing this could help families and other young adults who live with special needs, he would say, ‘Dad, what are you talking about? Why are you even asking me? It’s a no-brainer.”