Hayden Panettiere Dead at 36

8:33PM PT -- Law enforcement sources confirm police responded to an incident involving Hayden Sunday and there is currently an open investigation.

8:20PM PT -- A source close to Hayden tells TMZ ... she recently had been complaining about back pain in the past year.

Hayden Panettiere, best known for her roles in "Heroes" and "Nashville," has died at 36, TMZ has learned.

Sources with direct knowledge tell TMZ ... Hayden passed away earlier on Sunday. We're told she and her on-again, off-again boyfriend Brian Hickerson flew from Los Angeles to the south on Saturday. Sources tell us Brian's family is aware.

"It is with profound sadness that we share the tragic passing of our beloved Hayden. She was an incredible light and a force of nature who brought immeasurable love and joy to all who knew her -- and to the millions who watched her onscreen," her rep said in a statement to ABC News.

Hayden became a household name as a child actress before landing her breakout role as cheerleader Claire Bennet on NBC's "Heroes." She later starred as country singer Juliette Barnes on "Nashville," earning multiple award nominations for her performance.

The late actress also appeared in the beloved "Scream" franchise ... including "Scream 4" and "Scream VI," and lent her voice to the video game "Until Dawn."

Hayden got an early career boost as a child actress with her role as Sheryl Yoast in the 2000 sports drama "Remember the Titans," where she appeared alongside Denzel Washington and helped establish herself as a young Hollywood talent.

Hayden's personal life was often the subject of intense public attention, and she became increasingly open about her struggles and recovery in recent years ... releasing her memoir, "This Is Me: A Reckoning," in which she reflected on her childhood fame, motherhood, mental health and the loss of her younger brother, Jansen Panettiere.

Jansen died in 2023 at age 28. Hayden later spoke candidly about the devastating impact of his death and the guilt she carried following his passing. Hayden was also mom to daughter Kaya, whom she shares with former fiancé Wladimir Klitschko.

We last saw Hayden at LaGuardia Airport in May with a friend ahead of her memoir release, keeping it mostly quiet through it all -- no big reveals, no denials ... just one very telling grin.

Further details surrounding Hayden's death were not immediately available.

Hayden was 36