Ukrainian boxer Wladimir Klitschko has spoken out following the sudden death of his ex, Hayden Panettiere.
The pair, who got engaged in 2013, had an on-off relationship for almost a decade. Their daughter, 11-year-old Kaya, was born in 2014 and lives in Europe with her father.
"Our family is going through a time of profound shock and grief," Klitschko wrote in an Instagram post on Aug. 18, alongside an old photo of the three of them together, smiling at the beach.
"The announcement of Hayden's tragic death saddens me deeply," he continued, adding that the 36-year-old actress "left this world far too soon."
Klitschko, who holds full custody of Kaya, wrote that while Panettiere was "no longer" his partner, she played "an important part" in his life.
"She built an incredible career through immense talent, while also facing the darker sides of a very demanding industry. Nothing will erase the times we shared or the place she had in our lives," Klitschko said.
Hayden Panettiere cause of death: How did the actress die?
Panettiere's representative confirmed her death to USA TODAY on Sunday, Aug. 16. A cause of death has not yet been shared.
"It is with profound sadness that we share the tragic passing of our beloved Hayden," her father, Skip Panettiere, said in a statement.
The circumstances surrounding the "Nashville" star's death remain under investigation by the Greenville Police Department and Greenville County Coroner's Office.
The Greenville Police Department confirmed to USA TODAY that the actress was found unresponsive at Judson Mill Lofts in Greenville, South Carolina. According to 911 dispatch audio obtained by TMZ, emergency responders referenced a possible overdose and cardiac arrest while responding to the call.
Panettiere on the dark side of her career, childhood fame
In her memoir "This Is Me: A Reckoning," released in the months before her shock passing, Panettiere documented years of addiction, abuse and the fractured relationship with her mother, Lesley Vogel. She also wrote that she was "groomed" to be a "little soldier" throughout her early career, which began in front of the cameras as a baby.
Panettiere wrote that as a teenager, her team gave her "happy pills" – an amphetamine, Panettiere believed – before interviews and red carpets to help her focus. She said it was this habit that would "forever change" her world, ushering her towards addiction.
The memoir also explores the grief Panettiere felt following the death of her younger brother and "best friend," Jansen Panettiere, who she said was taking drugs, including crack and heroin, before he died.
Hayden Panettiere gave emotional interview about Kaya weeks before death
Just weeks before her death, Panettiere opened up about the complex but loving relationship between her and daughter Kaya, telling parenting magazine Momé in a July interview that the near-death birth in 2014 prompted severe postpartum depression and a reliance on alcohol to combat feelings of emptiness.
When Kaya turned 2, Klitschko requested full custody, citing worries about her being in Panettiere's care.
Panettiere spoke of entering rehab and putting her daughter's needs first.
"I knew I needed to be able to put her first so that I could get the help I needed and be the mom she needed me to be," she said, adding that the two of them frequently connect over FaceTime but that relinquishing custody was an incredibly painful decision.
"One day she'll understand my story, and why I wasn't able to be with her all the time," Panettiere told the magazine.
In his Instagram tribute, Klitschko vowed that he would always speak to Kaya about her mother "with respect and make sure she remembers the person she was."
Contributing: Sameen Chaudhry, Clare Mulroy, Anika Reed, USA TODAY
If you or someone you know is struggling or in crisis, you can call the Substance Abuse and Mental Health Services Administration Helpline at 1-800-662-HELP (4357).
This article originally appeared on USA TODAY: Wladimir Klitschko speaks of 'profound shock' over death of Hayden Panettiere
