Frankie Muniz has opened up about why he stopped talking to former co-star Hilary Duff, admitting the fallout stemmed from her mother.

The "Malcolm in the Middle" star revealed the story during the Sept. 2 episode of "The Joe Vulpis Podcast."

"Hilary Duff was probably one of my first friends when I moved to LA to film Malcolm [in the Middle]," Muniz recalled.

The two were introduced through mutual friends who lived in a Burbank, California, apartment complex popular with child actors, PageSix reported.

"We became really, really good friends. We had a really great relationship for a long time," he added.

Their friendship grew as Duff, then 38, invited Muniz to appear on her Disney show "Lizzie McGuire" in 2002, where he played himself. But Muniz quickly noticed a challenge: Hilary's mom, Susan Duff.

"She was intense. Hilary was so cool, we had an awesome relationship, but her mom was super intense. My mom was the opposite," Muniz said.

Frankie Muniz Opens Up About Falling Out with Hilary Duff

The tension escalated while filming the 2003 movie "Agent Cody Banks." Muniz explained that the role of Natalie Connors, his love interest in the film, had initially been intended for another actress, Kristin Kreuk from "Smallville."

According to People, but the next day, he learned from Susan that Hilary would be playing the role. "Needless to say, I wasn't thrilled about it. And not because I didn't want it to be Hilary," Muniz said.

He felt blindsided because his contract gave him a say in casting his on-screen love interest, but the studio assumed his friendship with Duff made it okay.

Despite the tension behind the scenes, Muniz shared that working on the film was still a positive experience for him.

He recalled having a great time during production, although he admitted feeling uncomfortable whenever Duff's mother visited the set.

After filming wrapped, the two never spoke again. "I've not said one word to her since then. So that's the truth of that," he admitted.

Looking back, Muniz admitted he regretted how things ended between him and Duff. He said he wished he had kept their friendship intact, describing it as special and lasting for years.

However, he noted that tensions involving Duff's mother had frustrated him at the time, which ultimately affected their relationship.

He also expressed hope for reconciliation, noting, "I would love to catch up with her... I'm sure she doesn't know any of that happened."

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Hilary Duff