Ethan Hawke opens up about parenting with ex-wife Uma Thurman, and about his new book, Rules for a Knight Credit: Jemal Countess/Getty Images

He's an Academy Award-nominated actor, writer, and director, but there's a role that Ethan Hawke is even prouder of — being father to his four children, who range in age from 4 to 17.

Hawke's kids were the inspiration for his newly released book, Rules for a Knight, which features advice for his two teenagers with ex-wife Uma Thurman, and younger daughters with current wife, Ryan Hawke.

"We started this as a Christmas present to my kids," the 45-year-old explained during a Hearst Master Class Q&A in NYC on Tuesday, Nov. 10.

Hawke, who divorced his Gattaca costar Thurman in 2005 after seven years of marriage, said that his current wife, Ryan, was reading a book about "how hard it is to be a stepparent," and the book grew from there.

"One of the things that’s really hard about parenting from a divorced standpoint, is that your kids can wreak havoc over you because there is a lot of, 'At Mommy’s house we have ice cream all the time' and 'I don’t think I’m going to come next weekend,'" he said. "There are rules at school, rules at Grandma’s house, rules at Mom’s house, rules at Dad’s house, nobody’s bad or has the right rules, they are just rules. So [Ryan and I] got on this riff about rules."

The Boyhood star wrote the book from the point of view of a knight who, fearing he won't return from battle, writes a letter to his children that's full of life lessons about forgiveness, honesty, courage, pride, and patience. Each chapter starts with a quote and is followed by a story related to it, and Ryan created the book’s illustrations.

"I don't nearly get to spend as much time with my kids as I like," he admitted. "The truth about the genesis of this book is that when you get your kids every other weekend, there aren’t many boring moments. So much of the best stuff out of my life is when you are bored and have nothing to do, and I always have something to do. I have the kids on this day, have to give them back another day, then they have this party, then soccer practice, and then they are gone. I never got to talk to them about these things, it’s like it never happened. It’s like when they leave on a Sunday afternoon and I say, 'Well, let me tell you why you shouldn’t lie.' It was a way for me to tell them these things in a book so that those types of conversations don’t get lost."

The book features quotes that Hawke has collected over the years. "I don’t claim to have any nuggets of wisdom, anything in this is something that I’ve read," he said. "I just love the idea of collecting what everybody else has learned and also love parables. It is the aspiring Jedi in me to hear people speak in parables, it's like, 'What the hell did that mean?' It gets your brain working in a nice way. I've just been collecting them my entire life, which I get to offer my kids, and now offer to you."

Want stories like these delivered straight to your inbox? Sign up now for the Us Weekly newsletter!