Hayden Panettiere speaks about her brother's death in her first interview (exclusive)

2023 should be a very good year for actress Hayden Panettiere.

The Amber Alert Star, who struggled with drug and alcohol addiction for years, was clean and sober after a stint at an inpatient rehab facility in early 2020. She was also single after emerging from an abusive on-off relationship with her ex-boyfriend and was grateful to be back at work on July 2. Scream 6.

Then, just three weeks before the film's premiere in February 2023, the unthinkable happened: her beloved younger brother Jansen died unexpectedly from an undiagnosed heart condition at just 28 years old. Panettiere's world collapsed.

“He was my only brother and my job was to protect him,” she tells PEOPLE in a new interview for this week's cover story. “When I lost him, it felt like I lost half my soul.”

Panettiere, 35, soon decided she didn't want to leave the house anymore, especially after being followed by photographers in the days following his death.

“I had to look at horrific paparazzi photos of myself coming out of Jansen's funeral, which was in a very private place, and that was shocking,” she says. “My agoraphobia, which I've struggled with in the past, came to the fore.”

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Adding to her grief, Panettiere's body reacted physically to the shock and within days was barely recognizable. “I'm just bloated,” she says of the rapid weight gain she experienced.

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She says the “stress and cortisol” coursing through her body caused the change that lowered her self-esteem. “I didn't feel confident enough to get dressed and leave the house, but I also knew I had to get out and keep moving or I would never stop looking and feeling that way,” she says.

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He added: “It became a destructive hamster wheel of asking: Do I feel good enough to go out?”

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She wanted to get back to work, but had to find the courage to break out of her rut. When her publicist introduced her to personal trainer Marnie Alton last year, she says everything changed for the better.

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Panettiere slowly began training with Alton, with whom she immediately developed trust and a close bond. She especially loved the long walks they took, during which they talked and Panettiere told stories from her past.

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“Those long, beautiful walks where we could let off steam were like a therapy session,” she says. “Marnie gave me strength.” The endorphins Panettiere got from burning fat also lifted her mood.

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“My body just responded, and not just to the workout. I was able to let go of the stress and the high expectations I'd always had of myself,” she says. As her insecurities faded, so did her agoraphobia. “There's nothing better than looking in the mirror and feeling like you look good enough to walk out the door,” she says.

She is still learning to live with the loss, but explains the new perspective she has gained since Jansen's death. “When something this big happens to you, you really learn to pick your battles and not get upset by the little things,” she says. “Because once something this horrible, this deep, this catastrophic happens to you, there's not much that can really shake you.”

Although she is looking forward to the release of her new film Amber Alert (in cinemas on September 27th) Above all, she is grateful that she feels more like herself every day. But that doesn't mean that she has overcome the trauma of Jansen's death or that she ever will.

“It will always break my heart. I will never get over it,” she says. “No matter how many years pass, I will never get over his loss.”

To read more about Hayden Panettiere's life, pick up the latest issue of PEOPLE on newsstands Friday.

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