After a challenging journey, Hayden Panettiere was finally in a place of sobriety, single, and ready to embrace new opportunities in her career when she faced an unimaginable loss: the sudden death of her beloved younger brother.

2023 was supposed to be a very good year for actress Hayden Panettiere.

The Amber Alert star, who for years had struggled with drugs and alcohol addiction, was clean and sober after spending time at an in-patient rehab facility in early 2020. She was also single, coming out of an abusive on-and-off relationship with her ex-boyfriend and was grateful to be back at work on Scream 6.

Then, just three weeks before the film’s premiere in February 2023, the unthinkable happened: Her beloved younger brother Jansen died unexpectedly of an undiagnosed heart condition at just 28. Panettiere’s world was shattered.

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

being followed by photographers in the days after his death.

“I had to see horrific paparazzi pictures of myself coming out of Jansen’s funeral, which happened in a very private place, and it was shocking,” she says. “My agoraphobia came out, which is something I’ve struggled with in the past.”

Compounding her grief, Panettiere’s body physically reacted to the shock, and within days she became virtually unrecognizable. “I just ballooned out,” she says of the rapid weight gain she experienced.

She says the “stress and cortisol” going through her body resulted in the change, which diminished her self esteem. “I didn’t feel confident to put on clothes and get out of the house, but I also knew that I needed to get out and keep moving or I’d never stop looking and feeling this way,” she says.

Adding, “It became a destructive hamster wheel of, do I feel good enough to go out?”

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

Panettiere started slowly training with Alton, with whom she shared an immediate trust and connection. She especially loved the long walks they would take, where they’d just talk and Panettiere would share her stories from the past.

These long, beautiful walks where we could vent and it would be this therapy session,” she says. “Marnie empowered me.” The endorphins Panettiere was getting from burning fat elevated her mood, too.

“My body just started reacting, not just from the working out. It allowed me to release the stress, the high expectations I’d always put on myself,” she says. As her insecurities faded, so did her agoraphobia. “There’s nothing like looking in the mirror and feeling like you look good enough to walk out the door,” she says. 

She’s still learning how to live with loss but explains the new perspective she gained following Jansen’s death. “When something that massive has happened to you, you really learn to pick your fights and just not let the little things upset you,” she shares. “Because once something so horrific, so deep, so catastrophic happens in your life, there’s not much that can really rock you.”

Though she’s looking forward to the release of her new movie Amber Alert (in theaters Sept. 27) she’s mostly just grateful that she’s feeling more and more like herself every day. That doesn’t mean she’s healed from the trauma of Jansen’s death, or ever will be.

will always be heartbroken about it. I will never be able to get over it,” she says. “No matter how many years go by, I will never get over his loss.”