Hayden Panettiere Talks About Her Brother Jansen's Death for First Time

Hayden Panettiere is speaking out for the first time about her brother Jansen’s death last year, saying she felt like it was her job to protect her only sibling ... and losing him was like losing half her soul.

The actress also shared her body reacted so strongly to Jansen’s death from an undiagnosed heart condition at 28, she gained a bunch of weight within days ... due to stress and cortisol surges coursing through her body.

Hayden told PEOPLE her changing appearance hit her self-esteem hard, making her feel insecure about leaving the house. She felt trapped in a "destructive hamster wheel" of needing to keep moving while battling those feelings.

She eventually got her confidence back with the help of her personal trainer, Marnie Alton ... who helped her shed stress and insecurities, and now she’s on track to feeling like herself again.

As for her brother's death, she's still grappling with the loss and says it's a heartbreak she'll always carry.