Wladimir Klitschko is mourning the death of his former fiancée, actress Hayden Panettiere, while making a heartfelt promise about how he will keep her memory alive for their daughter, Kaya.

The former heavyweight boxing champion shared an emotional tribute following Panettiere’s death at age 36, saying his family is experiencing “profound shock and grief.”

“She left this world far too soon,” Klitschko, 50, wrote on Instagram.

Although their romantic relationship ended years ago, Klitschko made it clear that Panettiere remained an important part of his life and family because of their shared daughter.

“To our daughter Kaya, I will always speak of her mother with respect and make sure she remembers the person she was,” he wrote.

That promise carries added meaning in light of what Panettiere said just weeks before her death—in a July interview with Fox News Digital, the “Heroes” and “Nashville” star revealed that she and Klitschko had agreed to raise their daughter despite no longer being together.

“We made a promise to each other that we would never say a bad word about each other to our child,” Panettiere said. “That was something that I grew up with. And we’ve stuck to that.”

Panettiere died Sunday in Greenville, South Carolina. First responders found her in cardiac arrest and attempted to resuscitate her before she was pronounced dead, according to the Greenville County Coroner’s Office. A preliminary autopsy found no signs of trauma that contributed to her death. Her cause and manner of death remain pending as authorities continue their investigation.

Panettiere and Klitschko welcomed Kaya in 2014. Four years later, Panettiere transferred custody of their daughter to Klitschko as she struggled with addiction and other personal challenges.

The actress later described the decision as deeply painful but said she believed it was best for Kaya. Seeing the support system her daughter had in Europe convinced her that a public custody battle between two famous parents could cause lasting harm.

“I know she’s safe. I know she’s well taken care of — beyond well taken care of,” Panettiere said.

She also acknowledged the emotional toll of living apart from her daughter, saying she tried to numb the pain but continued “putting one foot in front of the other somehow.”

Klitschko’s tribute also remembered Panettiere for the career she built after entering show business as a baby.

“She built an incredible career through immense talent, while also facing the darker sides of a very demanding industry,” he wrote.

Panettiere appeared in “Remember the Titans,” “Ice Princess,” and “Bring It On: All or Nothing” before becoming widely known as Claire Bennet on NBC’s “Heroes.” She later earned acclaim playing country singer Juliette Barnes on “Nashville.”

Klitschko said their separation could never erase the years they shared or Panettiere’s place in their family. Now, as their daughter faces life without her mother, he intends to make sure those memories endure.

“Young and talented people like Hayden should not leave this world so soon,” Klitschko wrote. “Rest easy, Hayden. May you find eternal peace.”