Tom Cruise tapped into his emotions on The Last Samurai by thinking about his son Connor.

In Ed Zwick’s memoir Hits, Flops, and Other Illusions: My Fortysomething Years, the director, 71, recalled his observations about Cruise’s soft spots while filming the 2003 period drama.

He said he noticed Cruise was “sweet and attentive” to a young actor in an earlier scene and that he was close to his then-8-year-old son Connor, whom he shares with ex-wife Nicole Kidman.

Aiming to evoke more natural emotion from Cruise, now 61, for a scene, Zwick pulled the actor aside and asked him to talk about Connor.

” ‘Tell me about your son,’ I said. He looked at me, surprised. I knew Connor had just returned to L.A. and Tom wouldn’t be seeing him for a while. For a moment Tom was quiet. And then he began to talk. It doesn’t matter what he said in those few short moments in the fading light. I watched as he looked inward, and a window seemed to open and his eyes softened,” wrote Zwick.

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With the daylight fading, the upcoming take was on a time crunch — and Cruise eventually “nailed the scene.”

On their way off set, Zwick remembers making eye contact with the actor and Cruise mouthing to him a “thank you.”

Despite his stardom, Cruise has often opted to keep his personal life private, including details about his kids. He and Kidman, 56, share Isabella, 31, and Connor, 29. From his marriage to Katie Holmes, he also has daughter Suri, now 17.

Hits, Flops, and Other Illusions: My Fortysomething Years is available now wherever books are sold.