Colin Farrell cried when his son took his first steps

Colin Farrell cried when his son took his first steps.

The 48-year-old actor's eldest child James, now 20, suffers from Angelman syndrome - a rare genetic disorder which involves delayed development - and he will "never forget" when the boy walked unaided for the first time, two weeks before his fourth birthday.

Colin recalled to People magazine: “[His occupational therapist said] 'James has something to show you.'

"I knew they were working on walking. And I stood over there, and she let him go, and he just came to... 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."

The 'Lobster' star told how a lot of families with children who have Angelman syndrome are told their kids may never walk.

He added: "So to see those first steps was just . . . I’ll never forget it. It was so overwhelmingly beautiful."

Colin praised James - who is non-verbal - for having "worked so hard all his life, so hard" and he feels proud of his son's achievements every day.

He said: "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."

The 'Banshees of Inisherin' actor - who has James with Kim Bordenave and 14-year-old Henry with actress Alicja Bachleda-Curus - told how his son's condition was initially misdiagnosed after he failed to hit developmental milestones.

He said: "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.

"It was a common misdiagnosis because it shared a lot of the same characteristics."