Actress Hayden Panettiere, known for her roles in "Heroes" and "Nashville," died on Sunday at the age of 36, her ex-fiancé Wladimir Klitschko said Tuesday. Panettiere "left this world far too soon," Klitschko stated in a social media post.

He described Panettiere as "an important part of my life and the mother of our daughter, Kaya." Klitschko, a former heavyweight boxing champion, added, "The announcement of Hayden’s tragic death saddens me deeply."

The Greenville County Coroner's Office confirmed that Panettiere was found in cardiac arrest prior to her death. An autopsy was completed, and the coroner's office stated that no signs of trauma contributing to her death were discovered. The official cause and manner of her death remain pending further investigation and additional studies.

Panettiere, who began her career as a child star, achieved widespread recognition for her portrayal of Claire Bennet in the NBC series "Heroes" and later as Juliette Barnes in the musical drama "Nashville." She was the mother of one child, Kaya Klitschko, born in 2014, with Klitschko.

"To our daughter Kaya, I will always speak of her mother with respect and make sure she remembers the person she was," Klitschko said. He extended his condolences to Panettiere's parents, friends, and fans, emphasizing that "young and talented people like Hayden should not leave this world so soon."

Klitschko shared a photograph of himself with Panettiere and requested privacy during this difficult time. Panettiere had been open about her personal struggles, which she detailed in her memoir, "This Is Me: A Reckoning," released in May. The book offered insights into her experiences with postpartum depression, addiction, recovery, trauma, domestic abuse, and loss. Klitschko acknowledged her ability to build a successful career while navigating the challenges of a demanding industry, stating, "Nothing will erase the times we shared or the place she had in our lives."