Colin Farrell has described watching his son take his first steps just before his fourth birthday after opening up about his Angelman Syndrome in depth for the first time.

Colin’s son James, now 20, was born with the neurogenetic disorder, which causes developmental delays, impaired balance and other issues.

Detailing the ‘profound’ moment to PEOPLE magazine, Colin, 48, said: ‘I knew they [James’s carers] were working on walking. And I stood over there, and she let him go, and he just came to [me].

James’ condition is severe enough that he is nonverbal and requires the help of a live-in caregiver to accomplish his day-to-day tasks.

The actor shares James with his ex, Canadian model Kim Bordenave, and has another son called Henry, 14, with Alicja Bachleda-Curús, his co-star in the 2009 film Ondine.

When James was four, Colin went public with his Angelman Syndrome, saying his son had demonstrated ‘amazing courage’ in the face of his condition.

In later went on to reveal that he and James’ mother make sure to  share in the smallest victories’ and enjoy the milestones whatever age they happen – including James’ the first words at age six , being able to feed himself at 19, and getting his seizures under control.

Colin has maintained a very private life and has not spoken about his son in great detail until recently although he told InStyle he first decided ‘talk publicly about the pride and joy I had in our son’ while attending the 2007 Special Olympics’

He said: ‘He has enriched my life, but I don’t want to minimize the trials that so many families go through; the fear, consternation, frustration, and pain… When you’re the parent of a child with special needs, it’s important to feel that you’re not alone.’

Discussing being a parent to a child with disabilities the Hollywood star said that James was the main reason he was able to get sober.

He explained that it was important for him to be fully sober in order to care for his son’s specific needs.

‘So James was about two when I got clean, when I got sober and he was a big big part of me putting the bottle down, a big part of it.’ he said.

‘Because I was in no condition to be a friend never mind the father of a child which such exacting needs. So if it wasn’t for my sobriety, I wouldn’t be able to be there for James and enjoy in the marvels of his life and support him in the way that I feel that can … ‘

Colin added: ‘I don’t want to make out like I’m the perfect dad, I f**k up left, right and centre but at least you have to be present to f**k up so I’m around, but yeah they’re very conjoined – my sobriety and my children …’.

The actor also revealed that his son, who lives full time at his home with a carer, is like a regular 20-year-old and the pair go swimming, go out for meals and watch films but added that the help of a live in carer has allowed him to be flexible and work.

He added: ‘He has a good life, he’s a happy young man… I’m proud of him every day.’

The Banshees of Inisherin actor has recently revealed his desire to speak more publicly about his son’s condition.

In an interview with People, he said he wanted the world to be kind to his son who has worked extremely hard to develop as best he can including learning repetition and balance.

He recalled the first time his son was able to feed himself and described the scene as like a Jackson Pollack painting but added that he’s proud of him every day ‘because I think he’s magic’.

Part of the reason he started the is that when people with special needs turn 21, they become ineligible for certain aid that was previously available to them.

But the actor also explained that there are fewer supports for those with disabilities after they turn 21 and that has pushed him on to create his charitable foundation.

He explained: ‘Once your child turns 21, they’re kind of on their own. All the safeguards that are put in place, special ed classes, that all goes away, so you’re left with a young adult who should be an integrated part of our modern society and more often than not is left behind.’