In Kevin Costner's new movie, 'Horizon: An American Saga,' his son, Hayes, plays Nathaniel Kittredge.
Hayes Costner is ready for his close-up!
The 15-year-old son of Kevin Costner and Christine Baumgartner talked with ET's Cassie DiLaura from Monday's premiere of his new film, Horizon: An American Saga - Chapter 1, in Los Angeles, and spilled on working with his dad, who serves as co-writer, director and star of the movie.
"He trapped me," Hayes joked of having to spend quality time with his movie star father, 69. "I got to spend the whole day with him every day and just see him work... I had such a blast."
"I just thought it was really cool and it was an amazing experience," he shared, adding of watching the film back, "I was just really proud of my dad. He's been working so long. I could just only think about my dad in that moment."
Later in the night, ET chatted with Kevin, who responded to his son's "trapped" comments, saying, "I did. I figured out how to have him close. He's never going to look this young, he's never going to look this sweet and handsome. He's just going to grow into a young man and he's really good in the film."
Fans first got a look at Hayes' acting debut when Kevin and the team dropped a trailer for the film back in February. The project has been the Field of Dream actor's passion project for nearly three decades.
In the trailer, Hayes stars alongside Sienna Miller and a young actress, who seemingly plays his mother and sister, as the trio begins to retreat into the floorboards of a home. After helping to secure the woman and the young girl, the actor delivers his line, declaring he is staying behind.
"It's all right -- I'm gonna be with Dad," Hayes says, closing a trap door above the two ladies.
It appears the Horizon film set was a family affair in more ways than one. Earlier this week, ET spoke with Miller, 42, who shared that her 11-year-old daughter, Marlowe, was almost an extra on the film.
"My daughter came," Miller began before admitting, "She was gonna be an extra but she chickened out."
"She just got shy but it was a perfect set for kids to be on because there were animals everywhere and people in incredible costumes, and he's such a family guy," she said of Kevin. "I have this photograph of Marlowe and Kevin around the monitor and he's got one headphone in his ear and he gave her the other, he's got his arm 'round her and I have a picture from the back and it was so special. He's such a family guy."
How couldn't he be? Kevin is dad to seven children, three of whom he shares with Baumgartner. In total, the actor has four sons and three daughters: Annie, 39, Lily, 37, Joe, 36, Liam, 26, Cayden, 16, Hayes, 15, and Grace, 13. His eldest three children come from his relationship with ex-wife Cindy Silva, while he shares Liam with former partner Bridget Rooney.
With Chapter 1 hitting theaters this month, Chapter 2 coming in August and Chapter 3 and Chapter 4 currently in production, Kevin previously told ET the project is one of the biggest undertakings of his career.
According to the star, production on the final two chapters is "going well," and there is more to come.
"We've shot about 13 days of it and we're coming back in August to finish it off," Kevin said. "I saw [Chapter 2] yesterday, and I'm really happy to be able to say that it's just as good as 1, and maybe better."
All four parts take place across a timespan of 15 years in pre and post-Civil War United States and tell a story primarily focused on the "expansion and settlement of the American west," according to a synopsis for the movies. Kevin plays Hayes Ellison, a character he named after his son.
Watch the trailer for the movie in the player below:
As for how he is feeling about the release of Chapter 1, Hayes tells ET, "I'm very excited."
Horizon: An American Saga - Chapter 1 hits theaters on June 28.
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