Hayden Panettiere was experiencing loneliness and struggling during the filming of her final movie, "Sleepwalker," according to her co-star Justin Chatwin. Panettiere died Sunday at the age of 36.

Chatwin, 43, told People that when he reconnected with Panettiere for the 2025 project, she seemed different from their earlier interactions. "I’ve been sober for 15 years, so I know this world of addiction, and Hollywood — it takes, and it takes from youth," he stated.

He recalled Panettiere confiding in him about her life and her battles with addiction. "She was authentic with me about her life and she opened up about her struggles with addiction," Chatwin said. "And who knows where it comes from? Does it come from Hollywood? Does it come from home? And a lot of times, it’s both."

The film "Sleepwalker," which was released in January, dealt with the subject of domestic abuse. Chatwin suggested that this subject matter might have been particularly difficult for Panettiere, referencing her past relationship with Brian Hickerson. "She did mention it," he recalled, referring to the film's themes. "While I could tell she was struggling, I was like, ‘I don’t think it’s this movie.’ … She was really lonely."

Despite any personal difficulties, Chatwin noted Panettiere's professional demeanor. "I’m sure that everyone else is going to say ‘Oh, she’s amazing. She’s such a sweet person on set,’ because she was," he said. "But we’re trained to be actors, so we’re acting on set, you know? And she is sweet. She had a beautiful heart."

Chatwin added that he valued the times Panettiere seemed to let her guard down, describing her as "delightful and super open" and that they "had a great time together." He expressed sadness over her death, saying, "I’m just saddened that another one got taken down."

Gayle King, who interviewed Panettiere in May to promote her memoir, "This Is Me: A Reckoning," also observed that the actress was "clearly still struggling" at that time.

Panettiere died in South Carolina. Paramedics responded to a call about an unresponsive female who had seemingly suffered an overdose and cardiac arrest. Resuscitation efforts were unsuccessful, and she was pronounced dead. The Greenville County Coroner’s Office stated that her autopsy showed no signs of trauma, and her cause of death remains unknown.

Panettiere had reportedly traveled to South Carolina with Brian Hickerson, her on-again, off-again ex-boyfriend. Hickerson had previously pleaded no contest to two felony counts of injuring a spouse or girlfriend in 2021 related to incidents involving Panettiere. A judge denied his request to reduce the charges days before Panettiere's death.

A source told Page Six that if Hickerson was back in Panettiere's life, it was likely something she was keeping private from friends due to potential shame associated with returning to a past relationship after difficult times.

Hickerson has not yet commented on Panettiere’s death. Wladimir Klitschko, Panettiere’s ex and the father of their 11-year-old daughter Kaya, issued a tribute on Monday.