James McAvoy's "prime responsibility" is his son.
The 40-year-old actor - who has nine-year-old Brendan with ex-wife Anne-Marie Duff and is now dating Lisa Liberati - is "very involved" in raising his child and insists the youngster will always come ahead of his other commitments.
He said: "We co-parent, so I'm very involved in my child's upbringing. But I feel like there are three parts of me - there's the father, the actor and the partner. I'm happy when all three can co-habit in the same space but, you know, a child is your prime responsibility. That's what I feel like as a father.
"As soon as you make the decision to have a kid, that's more important than anything else. Career has to come second. Relationships come second, it seems. Everything has to come second."
The 'It Chapter Two' star turned 40 this year and though the milestone didn't make him "philosophical", he's beginning to experience the impact of ageing.
He told Britain's OK! magazine: "To be honest, I didn't get very philosophical when I turned 40. However, I do notice myself getting older. When I get injured, it doesn't disappear after a week or two.
"It sticks around a little longer and there are more aches and pains.
"Up until the age of 38, I felt the same as I did at 21. Now it's starting to change."
James doesn't usually do very much to celebrate his birthday.
He said: "I've never been big on birthdays, I usually ignore them as much as I can. I certainly didn't party for my 40th. I was ill, and the weather was bad.
"Every now and again, I've had a birthday party and it's been great but, in general, I usually breeze through them.
"I don't know when I take stock of my life really. I think I'm a bit too busy to take stock."