Billy Bob Thornton didn't know about one of his grandkids until she was 18 months old

On Wednesday's episode of Relatively Famous: Ranch Rules, the new E! reality show about celebrities' kids attempting to survive and work on a ranch, actor Billy Bob Thornton's son, Harry James Thornton, revealed he hid the fact that he had a second child from his dad for a year and a half.

"Okay, so I had Mia, and I think I was 19 and a half. I didn't know how to tell my dad about the second one. I didn't tell him for like a year and a half," laughed Harry. He added, "Yeah, I mean, I saw my dad, like, once or twice a week, and I never mentioned it."

Harry, who has two daughters named Mia and Nikita with his fiancée Magi, opened up to Redmond Parker Wednesday, as he told Ray Parker Jr.'s son that he didn't know how to tell his dad about his second daughter, because he was scared.

"I was scared to tell, like, I don't know how he's gonna take it. When I had my first child, Mia, I had to ask him for money, and I didn't want him to think that I was as immature as I was," explained Harry.

It's clear the 27-year-old really cares about what his dad thinks about him, as he shared, "My dad traveled a lot when we were kids, but it didn't matter how much he worked. He would always make time for me and my brother. Now that I'm a dad, I try to do the same thing my dad did for us. I'll do anything to make them happy. I love being a dad." However, Harry ultimately learned that hiding his second daughter from his dad was pointless because, in the end, Billy Bob wasn't mad at all.

"He's like, 'You should have told me. Why would I be mad?' Obviously I'm much older now, but when I had Nikita, my second one, I didn't tell him because I didn't want him to think that I was how I was when I was younger," shared Harry.

Video Transcript

HARRY JAMES THORNTON: OK so I had Mia. And I think I was 19 and 1/2. I didn't know how to tell my dad about the second one. I didn't tell him for like a year and a half.

REDMOND PARKER: What?

KYLIE MAR: On Wednesday's episode of "Relatively Famous Ranch Rules," the new E reality show about celebrities' kids attempting to survive and work on a ranch. Actor Billy Bob Thornton's 27-year-old son. Harry Thornton. Revealed he hid the fact that he had a second child from his dad for a year and a half.

HARRY JAMES THORNTON: Yeah, yeah. I mean, I saw him like maybe-- I saw my dad like once or twice a week. And I never mentioned it.

REDMOND PARKER: A year and a half?

HARRY JAMES THORNTON: Yeah. He didn't know the whole time.

KYLIE MAR: Harry, who has two daughters named Mia and Nikita with his fiancee, Maggie, said he didn't know how to tell his dad because he was scared.

HARRY JAMES THORNTON: I was scared. Like, I don't know how he's going to take it. Like, when I had my first child, Mia. I had to ask him for money and I didn't want him to think that I was as immature as I was.

KYLIE MAR: But Harry also said that hiding Nikita from his dad ended up being pointless because Billy Bob wasn't mad at all.

HARRY JAMES THORNTON: He was like, you should have told me. Like, why would I be mad?

[LAUGHING]

Obviously I'm much older now, but when I had Nikita my second one I didn't tell him because I didn't want him to think that I was how when I was younger.