“Lizzie McGuire” star Hilary Duff is mourning the loss of her on-screen father, Robert Carradine, who died by suicide after battling bipolar disorder for nearly two decades. He was 71.

“This one hurts. It’s really hard to face this reality about an old friend,” Duff wrote in an Instagram post early Tuesday morning.

“There was so much warmth in the McGuire family and I always felt so cared for by my on-screen parents. I’ll be forever grateful for that,” she continued. “I’m deeply sad to learn Bobby was suffering. My heart aches for him, his family, and everyone who loved him.”

Duff also shared a series of photos from their time on “Lizzie McGuire,” including a picture of the full McGuire family.

Carradine was best known for playing Sam McGuire, Lizzie’s dad, in the Duff-led Disney Channel comedy from 2001 to 2004. He also reprised the role for “The Lizzie McGuire Movie” in 2003. Jake Thomas, who played Lizzie’s brother, Matt also took to Instagram to honor Carradine, remembering him as “a talented actor, musician, and director.”

“I looked up to him growing up. And later in life, I came to realize he thought I was pretty neat, too. So I guess I was doing something right in his eyes,” Thomas added. “My heart is with Marika and Ian. Rest easy, Bobby. Love you.”

Actress LaLaine, who played Lizzie’s best friend, Miranda, said Carradine’s death left her feeling “f—ed up.”

“Thankful I had time with you, thankful for our last conversation, and your constant fatherly like support,” she said. “I love you Bobby.”

Carradine’s family confirmed his death on Monday with a statement to Deadline.

“In a world that can feel so dark, Bobby was always a beacon [of] light to everyone around him,” they said. “We are bereft at the loss of this beautiful soul and want to acknowledge Bobby’s valiant struggle against his nearly two-decade battle with Bipolar. We hope his journey can shine a light and encourage addressing the stigma that attaches to mental illness.”

Carradine’s brother, “Nashville” actor Keith Carradine, said he died by suicide, according to reports.

In 2009, his half brother, David Carradine, was found dead in the closet of a Bangkok hotel room naked “with a cord wrapped around his neck and genitals,” ABC News reported at the time. Authorities said evidence at the scene negated suicide as the cause of death, but instead suggested “dangerous sex practices.” He’d been in Thailand at the time to film “Stretch.”

Also an actor, he was 72 years old when he died.

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