Colin Farrell has opened up about how he reluctantly embraced the life changes brought on by fatherhood, after he became a parent to son James, now 13.

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“When my first son was born, I said, ‘It's not gonna change me,'" the Irish actor told ET's Lauren Zima at theFantastic Beasts and Where to Find Them junket in New York. “Like, that’s what a 3-month-old boy needs -- a 21-year-old drunk friend -- but I thought I was going to be that cool dad.”

“[Fatherhood] changes you, but you have to decide to let it change you,” the 40-year-old star continued. “James was about two or three by the time I went, ‘Why am I trying to not let this inform how my life is lived now? I should allow it to change me.'"

Having since welcomed a second son, 7-year-old Henry, Farrell says parenting has affected everything from his work to his emotions, and he relishes watching his boys deal with daily challenges like “schoolyard politics.”

“It changed what kind of actor I am,” he shared. “It's just enriched my life and I assume it's given me a greater degree of not only anxiety, but depth and compassion.”<p>“My favorite thing is just the honor of observing these two guys figure out their lives and try to navigate what is, at times, [a treacherous world,]” Farrell added. “Kids can be so mean and human beings are emotional, sensitive creatures, so it's fascinating to observe these two guys navigate their way through friends and enemies and schoolyard politics. It’s crazy, man. It's terrifying, but that's the best part -- to be there for them and try not to get in their way and mess them up too much.”

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While Farrell admits that it’s difficult to ensure his kids stay “away from the bad guys,” he endeavors to be an “open dad,” who his boys can always confide in.

The actor’s own relationship with his father wasn’t as open.

“It's funny -- I wanted a dad that would be open, who I could talk to about feelings and sh** and I didn't have that and now I'm like, ‘Talk to me about your feelings,’ and the kids are like, ‘Nah, I don't want to talk,’" Farrell said. "I think just [being] accessible is the best thing you can do for your kids.”

One thing his boys have been talking about -- Farrell’s latest role as Percival Graves in Fantastic Beasts and Where to Find Them.
The Harry Potter prequel hits theaters on Nov. 18 and Farrell is looking forward to having his sons watch the film.

“I think Henry's seen the trailer, and he just wanted to know if I was a good guy or bad guy,” Farrell shared. “It's great that the two lads can have a look at this because the majority of the work I’ve done hasn't been very suitable for [them].”

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Although Farrell is thrilled to star in a film that his children can watch, he says the boys were not the reason why he took the role. In fact, it turns out the True Detective star is a bit of a Potterhead, having dreamed of starring in the franchise for years!

“For years I had enjoyed the Potter films and looking at the slew of actors that graced the screen in Potter films, wished I was one of them,” he admitted. “So the opportunity to work within that world and play a wizard and have a wand -- I was like, ‘This could be fun.’ So I talked to David Yates, who is the gatekeeper for this universe, having directed the last four films, and it was kind of a no-brainer.”

See more on the newest addition to the Fantastic Beasts and Where to Find Them franchise’s cast, Johnny Depp, in the video below.

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